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Nyandele JP, Kibondo UA, Issa F, Van Geertruyden JP, Warimwe G, Jongo S, Abdulla S, Olotu A. Pre-vaccination monocyte-to-lymphocyte ratio as a biomarker for the efficacy of malaria candidate vaccines: A subgroup analysis of pooled clinical trial data. PLoS One 2023; 18:e0291244. [PMID: 37708143 PMCID: PMC10501550 DOI: 10.1371/journal.pone.0291244] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/23/2022] [Accepted: 08/24/2023] [Indexed: 09/16/2023] Open
Abstract
BACKGROUND Pre-vaccination monocyte-to-lymphocyte ratio was previously suggested as a marker for malaria vaccine effectiveness. We investigated the potential of this cell ratio as a marker for malaria vaccine efficacy and effectiveness. Effectiveness was investigated by using clinical malaria endpoint, and efficacy was investigated by using surrogate endpoints of Plasmodium falciparum prepatent period, parasite density, and multiplication rates in a controlled human malaria infection trial (CHMI). METHODS We evaluated the correlation between monocyte-to-lymphocyte ratio and RTS,S vaccine effectiveness using Cox regression modeling with clinical malaria as the primary endpoint. Of the 1704 participants in the RTS,S field trial, data on monocyte-to-lymphocyte ratio was available for 842 participants, of whom our analyses were restricted. We further used Spearman Correlations and Cox regression modeling to evaluate the correlation between monocyte-to-lymphocyte ratio and Whole Sporozoite malaria vaccine efficacy using the surrogate endpoints. Of the 97 participants in the controlled human malaria infection vaccine trials, hematology and parasitology information were available for 82 participants, of whom our analyses were restricted. RESULTS The unadjusted efficacy of RTS,S malaria vaccine was 54% (95% CI: 37%-66%, p <0.001). No correlation was observed between monocyte-to-lymphocyte ratio and RTS,S vaccine efficacy (Hazard Rate (HR):0.90, 95%CI:0.45-1.80; p = 0.77). The unadjusted efficacy of Whole Sporozoite malaria vaccine in the appended dataset was 17.6% (95%CI:10%-28.5%, p<0.001). No association between monocyte-to-lymphocyte ratio and the Whole Sporozoite malaria vaccine was found against either the prepatent period (HR = 1.16; 95%CI:0.51-2.62, p = 0.72), parasite density (rho = 0.004, p = 0.97) or multiplication rates (rho = 0.031, p = 0.80). CONCLUSION Monocyte-to-lymphocyte ratio alone may not be an adequate marker for malaria vaccine efficacy. Further investigations on immune correlates and underlying mechanisms of immune protection against malaria could provide a clearer explanation of the differences between those protected in comparison with those not protected against malaria by vaccination.
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Affiliation(s)
- Jane Paula Nyandele
- Global Health Institute, University of Antwerp, Antwerp, Belgium
- Ifakara Health Institute, Bagamoyo Clinical Trial Unit, Bagamoyo, Tanzania
| | - Ummi Abdul Kibondo
- Ifakara Health Institute, Bagamoyo Clinical Trial Unit, Bagamoyo, Tanzania
| | - Fatuma Issa
- Ifakara Health Institute, Bagamoyo Clinical Trial Unit, Bagamoyo, Tanzania
| | | | | | - Said Jongo
- Ifakara Health Institute, Bagamoyo Clinical Trial Unit, Bagamoyo, Tanzania
| | - Salim Abdulla
- Ifakara Health Institute, Bagamoyo Clinical Trial Unit, Bagamoyo, Tanzania
| | - Ally Olotu
- Ifakara Health Institute, Bagamoyo Clinical Trial Unit, Bagamoyo, Tanzania
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2
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Lind ML, Dorion M, Houde AJ, Lansing M, Lapidus S, Thomas R, Yildirim I, Omer SB, Schulz WL, Andrews JR, Hitchings MDT, Kennedy BS, Richeson RP, Cummings DAT, Ko AI. Evidence of leaky protection following COVID-19 vaccination and SARS-CoV-2 infection in an incarcerated population. Nat Commun 2023; 14:5055. [PMID: 37598213 PMCID: PMC10439918 DOI: 10.1038/s41467-023-40750-8] [Citation(s) in RCA: 8] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/04/2023] [Accepted: 08/07/2023] [Indexed: 08/21/2023] Open
Abstract
Whether SARS-CoV-2 infection and COVID-19 vaccines confer exposure-dependent ("leaky") protection against infection remains unknown. We examined the effect of prior infection, vaccination, and hybrid immunity on infection risk among residents of Connecticut correctional facilities during periods of predominant Omicron and Delta transmission. Residents with cell, cellblock, and no documented exposure to SARS-CoV-2 infected residents were matched by facility and date. During the Omicron period, prior infection, vaccination, and hybrid immunity reduced the infection risk of residents without a documented exposure (HR: 0.36 [0.25-0.54]; 0.57 [0.42-0.78]; 0.24 [0.15-0.39]; respectively) and with cellblock exposures (0.61 [0.49-0.75]; 0.69 [0.58-0.83]; 0.41 [0.31-0.55]; respectively) but not with cell exposures (0.89 [0.58-1.35]; 0.96 [0.64-1.46]; 0.80 [0.46-1.39]; respectively). Associations were similar during the Delta period and when analyses were restricted to tested residents. Although associations may not have been thoroughly adjusted due to dataset limitations, the findings suggest that prior infection and vaccination may be leaky, highlighting the potential benefits of pairing vaccination with non-pharmaceutical interventions in crowded settings.
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Affiliation(s)
- Margaret L Lind
- Department of Epidemiology of Microbial Diseases, Yale School of Public Health, New Haven, CT, USA.
| | - Murilo Dorion
- Department of Epidemiology of Microbial Diseases, Yale School of Public Health, New Haven, CT, USA
| | - Amy J Houde
- Connecticut Department of Correction, Wethersfield, CT, USA
| | - Mary Lansing
- Connecticut Department of Correction, Wethersfield, CT, USA
| | - Sarah Lapidus
- Department of Epidemiology of Microbial Diseases, Yale School of Public Health, New Haven, CT, USA
| | - Russell Thomas
- Department of Epidemiology of Microbial Diseases, Yale School of Public Health, New Haven, CT, USA
| | - Inci Yildirim
- Department of Epidemiology of Microbial Diseases, Yale School of Public Health, New Haven, CT, USA
- Department of Pediatrics, Yale School of Medicine, New Haven, CT, USA
| | - Saad B Omer
- Department of Epidemiology of Microbial Diseases, Yale School of Public Health, New Haven, CT, USA
- Yale Institute for Global Health, Yale School of Public Health, New Haven, CT, USA
- UT Southwestern, School of Public Health, Dallas, TX, USA
| | - Wade L Schulz
- Department of Internal Medicine, Yale School of Medicine, New Haven, CT, USA
- Department of Laboratory Medicine, Yale University School of Medicine, New Haven, CT, USA
| | - Jason R Andrews
- Division of Infectious Diseases and Geographic Medicine, Stanford University, Stanford, CA, USA
| | - Matt D T Hitchings
- Department of Biostatistics, College of Public Health & Health Professions, University of Florida, Gainesville, FL, USA
| | | | | | - Derek A T Cummings
- Department of Biology, University of Florida, Gainesville, FL, USA
- Emerging Pathogens Institute, University of Florida, Gainesville, FL, USA
| | - Albert I Ko
- Department of Epidemiology of Microbial Diseases, Yale School of Public Health, New Haven, CT, USA.
- Instituto Gonçalo Moniz, Fundação Oswaldo Cruz, Salvador, BA, Brazil.
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3
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Nikas A, Ahmed H, Zarnitsyna VI. Competing Heterogeneities in Vaccine Effectiveness Estimation. Vaccines (Basel) 2023; 11:1312. [PMID: 37631880 PMCID: PMC10458793 DOI: 10.3390/vaccines11081312] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2023] [Revised: 07/26/2023] [Accepted: 07/27/2023] [Indexed: 08/27/2023] Open
Abstract
Understanding the waning of vaccine-induced protection is important for both immunology and public health. Population heterogeneities in underlying (pre-vaccination) susceptibility and vaccine response can cause measured vaccine effectiveness (mVE) to change over time, even in the absence of pathogen evolution and any actual waning of immune responses. We use multi-scale agent-based models parameterized using epidemiological and immunological data, to investigate the effect of these heterogeneities on mVE as measured by the hazard ratio. Based on our previous work, we consider the waning of antibodies according to a power law and link it to protection in two ways: (1) motivated by correlates of risk data and (2) using a within-host model of stochastic viral extinction. The effect of the heterogeneities is given by concise and understandable formulas, one of which is essentially a generalization of Fisher's fundamental theorem of natural selection to include higher derivatives. Heterogeneity in underlying susceptibility accelerates apparent waning, whereas heterogeneity in vaccine response slows down apparent waning. Our models suggest that heterogeneity in underlying susceptibility is likely to dominate. However, heterogeneity in vaccine response offsets <10% to >100% (median of 29%) of this effect in our simulations. Our study suggests heterogeneity is more likely to 'bias' mVE downwards towards the faster waning of immunity but a subtle bias in the opposite direction is also plausible.
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Affiliation(s)
- Ariel Nikas
- Department of Microbiology and Immunology, Emory University School of Medicine, Atlanta, GA 30322, USA
| | - Hasan Ahmed
- Department of Biology, Emory University, Atlanta, GA 30322, USA;
| | - Veronika I. Zarnitsyna
- Department of Microbiology and Immunology, Emory University School of Medicine, Atlanta, GA 30322, USA
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4
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Nikas A, Ahmed H, Zarnitsyna VI. Competing Heterogeneities in Vaccine Effectiveness Estimation. ARXIV 2023:arXiv:2305.01737v2. [PMID: 37205263 PMCID: PMC10187365] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Subscribe] [Scholar Register] [Indexed: 05/21/2023]
Abstract
Understanding waning of vaccine-induced protection is important for both immunology and public health. Population heterogeneities in underlying (pre-vaccination) susceptibility and vaccine response can cause measured vaccine effectiveness (mVE) to change over time even in the absence of pathogen evolution and any actual waning of immune responses. We use a multi-scale agent-based models parameterized using epidemiological and immunological data, to investigate the effect of these heterogeneities on mVE as measured by the hazard ratio. Based on our previous work, we consider waning of antibodies according to a power law and link it to protection in two ways: 1) motivated by correlates of risk data and 2) using a within-host model of stochastic viral extinction. The effect of the heterogeneities is given by concise and understandable formulas, one of which is essentially a generalization of Fisher's fundamental theorem of natural selection to include higher derivatives. Heterogeneity in underlying susceptibility accelerates apparent waning, whereas heterogeneity in vaccine response slows down apparent waning. Our models suggest that heterogeneity in underlying susceptibility is likely to dominate. However, heterogeneity in vaccine response offsets <10% to >100% (median of 29%) of this effect in our simulations. Our methodology and results may be helpful in understanding competing heterogeneities and waning of immunity and vaccine-induced protection. Our study suggests heterogeneity is more likely to 'bias' mVE downwards towards faster waning of immunity but a subtle bias in the opposite direction is also plausible.
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Affiliation(s)
- Ariel Nikas
- Emory University School of Medicine, Department of Microbiology and Immunology, Atlanta, Georgia, United States of America
| | - Hasan Ahmed
- Emory University, Department of Biology, Atlanta, Georgia, United States of America
| | - Veronika I. Zarnitsyna
- Emory University School of Medicine, Department of Microbiology and Immunology, Atlanta, Georgia, United States of America
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5
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Corder RM, Arez AP, Ferreira MU. Individual variation in Plasmodium vivax malaria risk: Are repeatedly infected people just unlucky? PLoS Negl Trop Dis 2023; 17:e0011020. [PMID: 36634044 PMCID: PMC9836309 DOI: 10.1371/journal.pntd.0011020] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023] Open
Abstract
Extensive research has examined why some people have frequent Plasmodium falciparum malaria episodes in sub-Saharan Africa while others remain free of disease most of the time. In contrast, malaria risk heterogeneity remains little studied in regions where P. vivax is the dominant species. Are repeatedly infected people in vivax malaria settings such as the Amazon just unlucky? Here, we briefly review evidence that human genetic polymorphism and acquired immunity after repeated exposure to parasites can modulate the risk of P. vivax infection and disease in predictable ways. One-fifth of the hosts account for 80% or more of the community-wide vivax malaria burden and contribute disproportionally to onward transmission, representing a priority target of more intensive interventions to achieve malaria elimination. Importantly, high-risk individuals eventually develop clinical immunity, even in areas with very low or residual malaria transmission, and may constitute a large but silent parasite reservoir.
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Affiliation(s)
- Rodrigo M. Corder
- Department of Epidemiology and Biostatistics, University of California, Berkeley School of Public Health, Berkeley, California, United States of America
| | - Ana Paula Arez
- Global Health and Tropical Medicine (GHTM), institute of Hygiene and Tropical Medicine, NOVA University of Lisbon, Lisbon, Portugal
| | - Marcelo U. Ferreira
- Global Health and Tropical Medicine (GHTM), institute of Hygiene and Tropical Medicine, NOVA University of Lisbon, Lisbon, Portugal
- Department of Parasitology, Institute of Biomedical Sciences, University of São Paulo, São Paulo, Brazil
- * E-mail: ,
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6
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Domenech de Cellès M, Wong A, Andrea Barrero Guevara L, Rohani P. Immunological heterogeneity informs estimation of the durability of vaccine protection. J R Soc Interface 2022; 19:20220070. [PMID: 35611620 PMCID: PMC9131131 DOI: 10.1098/rsif.2022.0070] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/24/2022] [Accepted: 04/26/2022] [Indexed: 11/30/2022] Open
Abstract
Deciphering the properties of vaccines against an emerging pathogen is essential for optimizing immunization strategies. Early after vaccine roll-out, however, uncertainties about vaccine immunity raise the question of how much time is needed to estimate these properties, particularly the durability of vaccine protection. Here we designed a simulation study, based on a generic transmission model of vaccination, to simulate the impact of a breadth of vaccines with different mean (range: 10 months-2 years) and variability (coefficient of variation range: 50-100%) of the duration of protection. Focusing on the dynamics of SARS-CoV-2 in the year after start of mass immunization in Germany as a case study, we then assessed how confidently the duration of protection could be estimated under a range of epidemiological scenarios. We found that lower mean and higher heterogeneity facilitated estimation of the duration of vaccine protection. Across the vaccines tested, rapid waning and high heterogeneity permitted complete identification of the duration of protection; by contrast, slow waning and low heterogeneity allowed only estimation of the fraction of vaccinees with rapid loss of immunity. These findings suggest that limited epidemiological data can inform the duration of vaccine immunity. More generally, they highlight the need to carefully consider immunological heterogeneity when designing transmission models to evaluate vaccines.
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Affiliation(s)
| | - Anabelle Wong
- Infectious Disease Epidemiology group, Max Planck Institute for Infection Biology, 10117 Berlin, Germany
- Institute of Public Health, Charité—Universitätsmedizin Berlin, 10117 Berlin, Germany
| | - Laura Andrea Barrero Guevara
- Infectious Disease Epidemiology group, Max Planck Institute for Infection Biology, 10117 Berlin, Germany
- Institute of Public Health, Charité—Universitätsmedizin Berlin, 10117 Berlin, Germany
| | - Pejman Rohani
- Odum School of Ecology, University of Georgia, Athens, GA 30602, USA
- Department of Infectious Diseases, University of Georgia, Athens, GA 30602, USA
- Center for Influenza Disease & Emergence Research (CIDER), University of Georgia, Athens, GA 30602, USA
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7
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Huber JH, Koepfli C, España G, Nekkab N, White MT, Alex Perkins T. How radical is radical cure? Site-specific biases in clinical trials underestimate the effect of radical cure on Plasmodium vivax hypnozoites. Malar J 2021; 20:479. [PMID: 34930278 PMCID: PMC8686294 DOI: 10.1186/s12936-021-04017-1] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/06/2021] [Accepted: 12/08/2021] [Indexed: 12/01/2022] Open
Abstract
BACKGROUND Plasmodium vivax blood-stage relapses originating from re-activating hypnozoites are a major barrier for control and elimination of this disease. Radical cure is a form of therapy capable of addressing this problem. Recent clinical trials of radical cure have yielded efficacy estimates ranging from 65 to 94%, with substantial variation across trial sites. METHODS An analysis of simulated trial data using a transmission model was performed to demonstrate that variation in efficacy estimates across trial sites can arise from differences in the conditions under which trials are conducted. RESULTS The analysis revealed that differences in transmission intensity, heterogeneous exposure and relapse rate can yield efficacy estimates ranging as widely as 12-78%, despite simulating trial data under the uniform assumption that treatment had a 75% chance of clearing hypnozoites. A longer duration of prophylaxis leads to a greater measured efficacy, particularly at higher transmission intensities, making the comparison between the protection of different radical cure treatment regimens against relapse more challenging. Simulations show that vector control and parasite genotyping offer two potential means to yield more standardized efficacy estimates that better reflect prevention of relapse. CONCLUSIONS Site-specific biases are likely to contribute to variation in efficacy estimates both within and across clinical trials. Future clinical trials can reduce site-specific biases by conducting trials in low-transmission settings where re-infections from mosquito bite are less common, by preventing re-infections using vector control measures, or by identifying and excluding likely re-infections that occur during follow-up, by using parasite genotyping methods.
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Affiliation(s)
- John H Huber
- Department of Biological Sciences and Eck Institute for Global Health, University of Notre Dame, Notre Dame, IN, USA.
| | - Cristian Koepfli
- Department of Biological Sciences and Eck Institute for Global Health, University of Notre Dame, Notre Dame, IN, USA
| | - Guido España
- Department of Biological Sciences and Eck Institute for Global Health, University of Notre Dame, Notre Dame, IN, USA
| | - Narimane Nekkab
- Unité Malaria: Parasites et Hôtes, Département Parasites et Insectes Vecteur, Institut Pasteur, Paris, France
| | - Michael T White
- Unité Malaria: Parasites et Hôtes, Département Parasites et Insectes Vecteur, Institut Pasteur, Paris, France
| | - T Alex Perkins
- Department of Biological Sciences and Eck Institute for Global Health, University of Notre Dame, Notre Dame, IN, USA
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8
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Reuling IJ, Mendes AM, de Jong GM, Fabra-García A, Nunes-Cabaço H, van Gemert GJ, Graumans W, Coffeng LE, de Vlas SJ, Yang ASP, Lee C, Wu Y, Birkett AJ, Ockenhouse CF, Koelewijn R, van Hellemond JJ, van Genderen PJJ, Sauerwein RW, Prudêncio M. An open-label phase 1/2a trial of a genetically modified rodent malaria parasite for immunization against Plasmodium falciparum malaria. Sci Transl Med 2021; 12:12/544/eaay2578. [PMID: 32434846 DOI: 10.1126/scitranslmed.aay2578] [Citation(s) in RCA: 20] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/04/2019] [Accepted: 04/22/2020] [Indexed: 12/14/2022]
Abstract
For some diseases, successful vaccines have been developed using a nonpathogenic counterpart of the causative microorganism of choice. The nonpathogenicity of the rodent Plasmodium berghei (Pb) parasite in humans prompted us to evaluate its potential as a platform for vaccination against human infection by Plasmodium falciparum (Pf), a causative agent of malaria. We hypothesized that the genetic insertion of a leading protein target for clinical development of a malaria vaccine, Pf circumsporozoite protein (CSP), in its natural pre-erythrocytic environment, would enhance Pb's capacity to induce protective immunity against Pf infection. Hence, we recently generated a transgenic Pb sporozoite immunization platform expressing PfCSP (PbVac), and we now report the clinical evaluation of its biological activity against controlled human malaria infection (CHMI). This first-in-human trial shows that PbVac is safe and well tolerated, when administered by a total of ~300 PbVac-infected mosquitoes per volunteer. Although protective efficacy evaluated by CHMI showed no sterile protection at the tested dose, significant delays in patency (2.2 days, P = 0.03) and decreased parasite density were observed after immunization, corresponding to an estimated 95% reduction in Pf liver parasite burden (confidence interval, 56 to 99%; P = 0.010). PbVac elicits dose-dependent cross-species cellular immune responses and functional PfCSP-dependent antibody responses that efficiently block Pf sporozoite invasion of liver cells in vitro. This study demonstrates that PbVac immunization elicits a marked biological effect, inhibiting a subsequent infection by the human Pf parasite, and establishes the clinical validation of a new paradigm in malaria vaccination.
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Affiliation(s)
- Isaie J Reuling
- Radboud Center for Infectious Diseases, Department of Medical Microbiology, Radboud University Medical Center, 6525 GA Nijmegen, Netherlands
| | - António M Mendes
- Instituto de Medicina Molecular, Faculdade de Medicina, Universidade de Lisboa, Avenida Professor Egas Moniz, 1649-028 Lisboa, Portugal
| | - Gerdie M de Jong
- Department of Medical Microbiology and Infectious Diseases, Erasmus MC, 3015 GD Rotterdam, Netherlands
| | - Amanda Fabra-García
- Radboud Center for Infectious Diseases, Department of Medical Microbiology, Radboud University Medical Center, 6525 GA Nijmegen, Netherlands
| | - Helena Nunes-Cabaço
- Instituto de Medicina Molecular, Faculdade de Medicina, Universidade de Lisboa, Avenida Professor Egas Moniz, 1649-028 Lisboa, Portugal
| | - Geert-Jan van Gemert
- Radboud Center for Infectious Diseases, Department of Medical Microbiology, Radboud University Medical Center, 6525 GA Nijmegen, Netherlands
| | - Wouter Graumans
- Radboud Center for Infectious Diseases, Department of Medical Microbiology, Radboud University Medical Center, 6525 GA Nijmegen, Netherlands
| | - Luc E Coffeng
- Department of Public Health, Erasmus MC, University Medical Center Rotterdam, 3015 GD Rotterdam, Netherlands
| | - Sake J de Vlas
- Department of Public Health, Erasmus MC, University Medical Center Rotterdam, 3015 GD Rotterdam, Netherlands
| | - Annie S P Yang
- Radboud Center for Infectious Diseases, Department of Medical Microbiology, Radboud University Medical Center, 6525 GA Nijmegen, Netherlands
| | - Cynthia Lee
- PATH's Malaria Vaccine Initiative, Washington, DC 20001, USA
| | - Yimin Wu
- PATH's Malaria Vaccine Initiative, Washington, DC 20001, USA
| | | | | | - Rob Koelewijn
- Department of Medical Microbiology and Infectious Diseases, Erasmus MC, 3015 GD Rotterdam, Netherlands
| | - Jaap J van Hellemond
- Department of Medical Microbiology and Infectious Diseases, Erasmus MC, 3015 GD Rotterdam, Netherlands
| | - Perry J J van Genderen
- Department of Medical Microbiology and Infectious Diseases, Erasmus MC, 3015 GD Rotterdam, Netherlands. .,Corporate Travel Clinic Erasmus MC, 3015 CP Rotterdam, Netherlands
| | - Robert W Sauerwein
- Radboud Center for Infectious Diseases, Department of Medical Microbiology, Radboud University Medical Center, 6525 GA Nijmegen, Netherlands.
| | - Miguel Prudêncio
- Instituto de Medicina Molecular, Faculdade de Medicina, Universidade de Lisboa, Avenida Professor Egas Moniz, 1649-028 Lisboa, Portugal.
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Tokars JI, Patel MM, Foppa IM, Reed C, Fry AM, Ferdinands JM. Waning of Measured Influenza Vaccine Effectiveness Over Time: The Potential Contribution of Leaky Vaccine Effect. Clin Infect Dis 2021; 71:e633-e641. [PMID: 32227109 DOI: 10.1093/cid/ciaa340] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/07/2019] [Accepted: 03/26/2020] [Indexed: 02/05/2023] Open
Abstract
BACKGROUND Several observational studies have shown decreases in measured influenza vaccine effectiveness (mVE) during influenza seasons. One study found decreases of 6-11%/month during the 2011-2012 to 2014-2015 seasons. These findings could indicate waning immunity but could also occur if vaccine effectiveness is stable and vaccine provides partial protection in all vaccinees ("leaky") rather than complete protection in a subset of vaccinees. Since it is unknown whether influenza vaccine is leaky, we simulated the 2011-2012 to 2014-2015 influenza seasons to estimate the potential contribution of leaky vaccine effect to the observed decline in mVE. METHODS We used available data to estimate daily numbers of vaccinations and infections with A/H1N1, A/H3N2, and B viruses. We assumed that vaccine effect was leaky, calculated mVE as 1 minus the Mantel-Haenszel relative risk of vaccine on incident cases, and determined the mean mVE change per 30 days since vaccination. Because change in mVE was highly dependent on infection rates, we performed simulations using low (15%) and high (31%) total (including symptomatic and asymptomatic) seasonal infection rates. RESULTS For the low infection rate, decreases (absolute) in mVE per 30 days after vaccination were 2% for A/H1N1 and 1% for A/H3N2and B viruses. For the high infection rate, decreases were 5% for A/H1N1, 4% for A/H3, and 3% for B viruses. CONCLUSIONS The leaky vaccine bias could account for some, but probably not all, of the observed intraseasonal decreases in mVE. These results underscore the need for strategies to deal with intraseasonal vaccine effectiveness decline.
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Affiliation(s)
- Jerome I Tokars
- Influenza Division, Centers for Disease Control and Prevention, Atlanta, Georgia, USA
| | - Manish M Patel
- Influenza Division, Centers for Disease Control and Prevention, Atlanta, Georgia, USA
| | - Ivo M Foppa
- Influenza Division, Centers for Disease Control and Prevention, Atlanta, Georgia, USA.,Battelle, Atlanta, Georgia, USA
| | - Carrie Reed
- Influenza Division, Centers for Disease Control and Prevention, Atlanta, Georgia, USA
| | - Alicia M Fry
- Influenza Division, Centers for Disease Control and Prevention, Atlanta, Georgia, USA
| | - Jill M Ferdinands
- Influenza Division, Centers for Disease Control and Prevention, Atlanta, Georgia, USA
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10
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Martinez J, Showering A, Oke C, Jones RT, Logan JG. Differential attraction in mosquito-human interactions and implications for disease control. Philos Trans R Soc Lond B Biol Sci 2020; 376:20190811. [PMID: 33357061 PMCID: PMC7776937 DOI: 10.1098/rstb.2019.0811] [Citation(s) in RCA: 19] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022] Open
Abstract
Mosquito-borne diseases are a major burden on human health worldwide and their eradication through vector control methods remains challenging. In particular, the success of vector control interventions for targeting diseases such as malaria is under threat, in part due to the evolution of insecticide resistance, while for other diseases effective control solutions are still lacking. The rate at which mosquitoes encounter and bite humans is a key determinant of their capacity for disease transmission. Future progress is strongly reliant on improving our understanding of the mechanisms leading to a mosquito bite. Here, we review the biological factors known to influence the attractiveness of mosquitoes to humans, such as body odour, the skin microbiome, genetics and infection by parasites. We identify the knowledge gaps around the relative contribution of each factor, and the potential links between them, as well as the role of natural selection in shaping vector–host–parasite interactions. Finally, we argue that addressing these questions will contribute to improving current tools and the development of novel interventions for the future. This article is part of the theme issue ‘Novel control strategies for mosquito-borne diseases'.
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Affiliation(s)
- Julien Martinez
- Department of Disease Control, Faculty of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, Keppel Street, London WC1E 7HT, UK
| | - Alicia Showering
- Department of Disease Control, Faculty of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, Keppel Street, London WC1E 7HT, UK
| | - Catherine Oke
- Department of Disease Control, Faculty of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, Keppel Street, London WC1E 7HT, UK
| | - Robert T Jones
- Department of Disease Control, Faculty of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, Keppel Street, London WC1E 7HT, UK
| | - James G Logan
- Department of Disease Control, Faculty of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, Keppel Street, London WC1E 7HT, UK
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11
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Pitzer VE, Bennett A, Bar-Zeev N, Jere KC, Lopman BA, Lewnard JA, Parashar UD, Cunliffe NA. Evaluating strategies to improve rotavirus vaccine impact during the second year of life in Malawi. Sci Transl Med 2020; 11:11/505/eaav6419. [PMID: 31413144 DOI: 10.1126/scitranslmed.aav6419] [Citation(s) in RCA: 24] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/05/2018] [Revised: 02/08/2019] [Accepted: 07/25/2019] [Indexed: 01/08/2023]
Abstract
Rotavirus vaccination has substantially reduced the incidence of rotavirus-associated gastroenteritis (RVGE) in high-income countries, but vaccine impact and estimated effectiveness are lower in low-income countries for reasons that are poorly understood. We used mathematical modeling to quantify rotavirus vaccine impact and investigate reduced vaccine effectiveness, particularly during the second year of life, in Malawi, where vaccination was introduced in October 2012 with doses at 6 and 10 weeks. We fitted models to 12 years of prevaccination data and validated the models against postvaccination data to evaluate the magnitude and duration of vaccine protection. The observed rollout of vaccination in Malawi was predicted to lead to a 26 to 77% decrease in the overall incidence of moderate-to-severe RVGE in 2016, depending on assumptions about waning of vaccine-induced immunity and heterogeneity in vaccine response. Vaccine effectiveness estimates were predicted to be higher among 4- to 11-month-olds than 12- to 23-month-olds, even when vaccine-induced immunity did not wane, due to differences in the rate at which vaccinated and unvaccinated individuals acquire immunity from natural infection. We found that vaccine effectiveness during the first and second years of life could potentially be improved by increasing the proportion of infants who respond to vaccination or by lowering the rotavirus transmission rate. An additional dose of rotavirus vaccine at 9 months of age was predicted to lead to higher estimated vaccine effectiveness but to only modest (5 to 16%) reductions in RVGE incidence over the first 3 years after introduction, regardless of assumptions about waning of vaccine-induced immunity.
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Affiliation(s)
- Virginia E Pitzer
- Department of Epidemiology of Microbial Diseases, Yale School of Public Health, Yale University, New Haven, CT 06520-8034, USA.
| | - Aisleen Bennett
- Malawi-Liverpool-Wellcome Trust Clinical Research Programme, College of Medicine, University of Malawi, Blantyre 3, Malawi.,Centre for Global Vaccine Research, Institute of Infection and Global Health, University of Liverpool, Liverpool L69 3BX, UK
| | - Naor Bar-Zeev
- Malawi-Liverpool-Wellcome Trust Clinical Research Programme, College of Medicine, University of Malawi, Blantyre 3, Malawi.,International Vaccine Access Center, Department of International Health, Bloomberg School of Public Health, Johns Hopkins University, Baltimore, MD 21231, USA
| | - Khuzwayo C Jere
- Malawi-Liverpool-Wellcome Trust Clinical Research Programme, College of Medicine, University of Malawi, Blantyre 3, Malawi.,Centre for Global Vaccine Research, Institute of Infection and Global Health, University of Liverpool, Liverpool L69 3BX, UK.,Department of Medical Laboratory Sciences, College of Medicine, University of Malawi, Blantyre 3, Malawi
| | - Benjamin A Lopman
- Department of Epidemiology, Rollins School of Public Health, Emory University, Atlanta, GA 30322, USA.,Epidemiology Branch, Division of Viral Diseases, Centers for Disease Control and Prevention, Atlanta, GA 30329-4027, USA
| | - Joseph A Lewnard
- Division of Epidemiology, School of Public Health, University of California, Berkeley, Berkeley, CA 94720, USA
| | - Umesh D Parashar
- Epidemiology Branch, Division of Viral Diseases, Centers for Disease Control and Prevention, Atlanta, GA 30329-4027, USA
| | - Nigel A Cunliffe
- Centre for Global Vaccine Research, Institute of Infection and Global Health, University of Liverpool, Liverpool L69 3BX, UK
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12
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Corder RM, Ferreira MU, Gomes MGM. Modelling the epidemiology of residual Plasmodium vivax malaria in a heterogeneous host population: A case study in the Amazon Basin. PLoS Comput Biol 2020; 16:e1007377. [PMID: 32168349 PMCID: PMC7108741 DOI: 10.1371/journal.pcbi.1007377] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2019] [Revised: 03/31/2020] [Accepted: 01/29/2020] [Indexed: 02/07/2023] Open
Abstract
The overall malaria burden in the Americas has decreased dramatically over the past two decades, but residual transmission pockets persist across the Amazon Basin, where Plasmodium vivax is the predominant infecting species. Current elimination efforts require a better quantitative understanding of malaria transmission dynamics for planning, monitoring, and evaluating interventions at the community level. This can be achieved with mathematical models that properly account for risk heterogeneity in communities approaching elimination, where few individuals disproportionately contribute to overall malaria prevalence, morbidity, and onwards transmission. Here we analyse demographic information combined with routinely collected malaria morbidity data from the town of Mâncio Lima, the main urban transmission hotspot of Brazil. We estimate the proportion of high-risk subjects in the host population by fitting compartmental susceptible-infected-susceptible (SIS) transmission models simultaneously to age-stratified vivax malaria incidence densities and the frequency distribution of P. vivax malaria attacks experienced by each individual over 12 months. Simulations with the best-fitting SIS model indicate that 20% of the hosts contribute 86% of the overall vivax malaria burden. Despite the low overall force of infection typically found in the Amazon, about one order of magnitude lower than that in rural Africa, high-risk individuals gradually develop clinical immunity following repeated infections and eventually constitute a substantial infectious reservoir comprised of asymptomatic parasite carriers that is overlooked by routine surveillance but likely fuels onwards malaria transmission. High-risk individuals therefore represent a priority target for more intensive and effective interventions that may not be readily delivered to the entire community.
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Affiliation(s)
- Rodrigo M. Corder
- Department of Parasitology, Institute of Biomedical Sciences, University of São Paulo, São Paulo, Brazil
- * E-mail: (RMC); (MGMG)
| | - Marcelo U. Ferreira
- Department of Parasitology, Institute of Biomedical Sciences, University of São Paulo, São Paulo, Brazil
| | - M. Gabriela M. Gomes
- Liverpool School of Tropical Medicine, Liverpool, United Kingdom
- CIBIO-InBIO, Centro de Investigação em Biodiversidade e Recursos Genéticos, and CMUP, Centro de Matemática da Universidade do Porto, Porto, Portugal
- * E-mail: (RMC); (MGMG)
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13
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España G, Hogea C, Guignard A, ten Bosch QA, Morrison AC, Smith DL, Scott TW, Schmidt A, Perkins TA. Biased efficacy estimates in phase-III dengue vaccine trials due to heterogeneous exposure and differential detectability of primary infections across trial arms. PLoS One 2019; 14:e0210041. [PMID: 30682037 PMCID: PMC6347271 DOI: 10.1371/journal.pone.0210041] [Citation(s) in RCA: 68] [Impact Index Per Article: 13.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/10/2018] [Accepted: 12/14/2018] [Indexed: 01/20/2023] Open
Abstract
Vaccine efficacy (VE) estimates are crucial for assessing the suitability of dengue vaccine candidates for public health implementation, but efficacy trials are subject to a known bias to estimate VE toward the null if heterogeneous exposure is not accounted for in the analysis of trial data. In light of many well-characterized sources of heterogeneity in dengue virus (DENV) transmission, our goal was to estimate the potential magnitude of this bias in VE estimates for a hypothetical dengue vaccine. To ensure that we realistically modeled heterogeneous exposure, we simulated city-wide DENV transmission and vaccine trial protocols using an agent-based model calibrated with entomological and epidemiological data from long-term field studies in Iquitos, Peru. By simulating a vaccine with a true VE of 0.8 in 1,000 replicate trials each designed to attain 90% power, we found that conventional methods underestimated VE by as much as 21% due to heterogeneous exposure. Accounting for the number of exposures in the vaccine and placebo arms eliminated this bias completely, and the more realistic option of including a frailty term to model exposure as a random effect reduced this bias partially. We also discovered a distinct bias in VE estimates away from the null due to lower detectability of primary DENV infections among seronegative individuals in the vaccinated group. This difference in detectability resulted from our assumption that primary infections in vaccinees who are seronegative at baseline resemble secondary infections, which experience a shorter window of detectable viremia due to a quicker immune response. This resulted in an artefactual finding that VE estimates for the seronegative group were approximately 1% greater than for the seropositive group. Simulation models of vaccine trials that account for these factors can be used to anticipate the extent of bias in field trials and to aid in their interpretation.
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Affiliation(s)
- Guido España
- Department of Biological Sciences and Eck Institute for Global Health, University of Notre Dame, Notre Dame, IN, United States of America
| | - Cosmina Hogea
- GlaxoSmithKline, Rockville, MD, United States of America
| | | | - Quirine A. ten Bosch
- Department of Biological Sciences and Eck Institute for Global Health, University of Notre Dame, Notre Dame, IN, United States of America
| | - Amy C. Morrison
- United States Naval Medical Research Unit No. 6, Lima, Peru
- Department of Entomology and Nematology, University of California, Davis, CA, United States of America
| | - David L. Smith
- Institute for Health Metrics and Evaluation, University of Washington, Seattle, WA, United States of America
| | - Thomas W. Scott
- Department of Entomology and Nematology, University of California, Davis, CA, United States of America
| | | | - T. Alex Perkins
- Department of Biological Sciences and Eck Institute for Global Health, University of Notre Dame, Notre Dame, IN, United States of America
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14
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Wilson KL, Flanagan KL, Prakash MD, Plebanski M. Malaria vaccines in the eradication era: current status and future perspectives. Expert Rev Vaccines 2019; 18:133-151. [PMID: 30601095 DOI: 10.1080/14760584.2019.1561289] [Citation(s) in RCA: 28] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
INTRODUCTION The challenge to eradicate malaria is an enormous task that will not be achieved by current control measures, thus an efficacious and long-lasting malaria vaccine is required. The licensing of RTS, S/AS01 is a step forward in providing some protection, but a malaria vaccine that protects across multiple transmission seasons is still needed. To achieve this, inducing beneficial immune responses while minimising deleterious non-targeted effects will be essential. AREAS COVERED This article discusses the current challenges and advances in malaria vaccine development and reviews recent human clinical trials for each stage of infection. Pubmed and ScienceDirect were searched, focusing on cell mediated immunity and how T cell subsets might be targeted in future vaccines using novel adjuvants and emerging vaccine technologies. EXPERT COMMENTARY Despite decades of research there is no highly effective licensed malaria vaccine. However, there is cause for optimism as new adjuvants and vaccine systems emerge, and our understanding of correlates of protection increases, especially regarding cellular immunity. The new field of heterologous (non-specific) effects of vaccines also highlights the broader consequences of immunization. Importantly, the WHO led Malaria Vaccine Technology Roadmap illustrates that there is a political will among the global health community to make it happen.
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Affiliation(s)
- K L Wilson
- a Department of Immunology and Pathology, Faculty of Medicine, Nursing and Health Sciences , Monash University , Melbourne , Australia.,b School of Health and Biomedical Sciences , RMIT University , Bundoora , Australia
| | - K L Flanagan
- a Department of Immunology and Pathology, Faculty of Medicine, Nursing and Health Sciences , Monash University , Melbourne , Australia.,b School of Health and Biomedical Sciences , RMIT University , Bundoora , Australia.,c School of Medicine, Faculty of Health Sciences , University of Tasmania , Launceston , Australia
| | - M D Prakash
- b School of Health and Biomedical Sciences , RMIT University , Bundoora , Australia
| | - M Plebanski
- b School of Health and Biomedical Sciences , RMIT University , Bundoora , Australia
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15
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Elazzouzi A, Lamrani Alaoui A, Tilioua M, Tridane A. Global stability analysis for a generalized delayed SIR model with vaccination and treatment. ADVANCES IN DIFFERENCE EQUATIONS 2019; 2019:532. [PMID: 32226453 PMCID: PMC7100696 DOI: 10.1186/s13662-019-2447-z] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/10/2019] [Accepted: 12/03/2019] [Indexed: 05/18/2023]
Abstract
In this work, we investigate the stability of an SIR epidemic model with a generalized nonlinear incidence rate and distributed delay. The model also includes vaccination term and general treatment function, which are the two principal control measurements to reduce the disease burden. Using the Lyapunov functions, we show that the disease-free equilibrium state is globally asymptotically stable if R 0 ≤ 1 , where R 0 is the basic reproduction number. On the other hand, the disease-endemic equilibrium is globally asymptotically stable when R 0 > 1 . For a specific type of treatment and incidence functions, our analysis shows the success of the vaccination strategy, as well as the treatment depends on the initial size of the susceptible population. Moreover, we discuss, numerically, the behavior of the basic reproduction number with respect to vaccination and treatment parameters.
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Affiliation(s)
- A. Elazzouzi
- LSI Laboratory, FP Taza, Department of MPI, Sidi Mohamed Ben Abdellah University, Taza, Morocco
| | - A. Lamrani Alaoui
- MAMCS Group, M2I Laboratory, FST Errachidia, Moulay Ismaïl University of Meknès, Errachidia, Morocco
| | - M. Tilioua
- MAMCS Group, M2I Laboratory, FST Errachidia, Moulay Ismaïl University of Meknès, Errachidia, Morocco
| | - A. Tridane
- Department of Mathematical Sciences, United Arab Emirates University, Al Ain, United Arab Emirates
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16
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Pasin C, Halloran ME, Gilbert PB, Langevin E, Ochiai RL, Pitisuttithum P, Capeding MR, Carrasquilla G, Frago C, Cortés M, Chambonneau L, Moodie Z. Periods of high dengue transmission defined by rainfall do not impact efficacy of dengue vaccine in regions of endemic disease. PLoS One 2018; 13:e0207878. [PMID: 30543657 PMCID: PMC6292612 DOI: 10.1371/journal.pone.0207878] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/17/2018] [Accepted: 11/07/2018] [Indexed: 11/22/2022] Open
Abstract
OBJECTIVE To evaluate the association of rainy season with overall dengue disease incidence and with the efficacy of the Sanofi Pasteur recombinant, live, attenuated, tetravalent vaccine (CYD-TDV) in two randomized, controlled multicenter phase III clinical trials in Asia and Latin America. METHODS Rainy seasons were defined for each study site using climatological information from the World Meteorological Organization. The dengue attack rate in the placebo group for each study month was calculated as the number of symptomatic, virologically-confirmed dengue events in a given month divided by the number of participants at risk in the same month. Time-dependent Cox proportional hazard models were used to test whether rainy season was associated with dengue disease and whether it modified vaccine efficacy in each of the two trials and in both of the trials combined. FINDINGS Rainy season, country, and age were all significantly associated with dengue disease in both studies. Vaccine efficacy did not change during the rainy season in any of the analyses. CONCLUSIONS Although dengue transmission and exposure are expected to increase during the rainy season, our results indicate that CYD-TDV vaccine efficacy remains constant throughout the year in endemic regions.
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Affiliation(s)
- Chloé Pasin
- Université de Bordeaux, INSERM U1219 Bordeaux Population Health center, INRIA SISTM, Bordeaux, France
- Vaccine Research Institute, Creteil, France
- ENS Cachan, Université Paris-Saclay, Cachan, France
| | - M. Elizabeth Halloran
- Fred Hutchinson Cancer Research Center, Seattle, Washington, United States of America
- University of Washington, Seattle, Washington, United States of America
| | - Peter B. Gilbert
- Fred Hutchinson Cancer Research Center, Seattle, Washington, United States of America
- University of Washington, Seattle, Washington, United States of America
| | | | | | - Punnee Pitisuttithum
- Vaccine Trial Centre and Department of Clinical Tropical Medicine, Faculty of Tropical Medicine, Mahidol University, Nakorn Pratum, Thailand
| | | | | | | | | | | | - Zoe Moodie
- Fred Hutchinson Cancer Research Center, Seattle, Washington, United States of America
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17
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Temporally Varying Relative Risks for Infectious Diseases: Implications for Infectious Disease Control. Epidemiology 2018; 28:136-144. [PMID: 27748685 DOI: 10.1097/ede.0000000000000571] [Citation(s) in RCA: 29] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
Risks for disease in some population groups relative to others (relative risks) are usually considered to be consistent over time, although they are often modified by other, nontemporal factors. For infectious diseases, in which overall incidence often varies substantially over time, the patterns of temporal changes in relative risks can inform our understanding of basic epidemiologic questions. For example, recent studies suggest that temporal changes in relative risks of infection over the course of an epidemic cycle can both be used to identify population groups that drive infectious disease outbreaks, and help elucidate differences in the effect of vaccination against infection (that is relevant to transmission control) compared with its effect against disease episodes (that reflects individual protection). Patterns of change in the age groups affected over the course of seasonal outbreaks can provide clues to the types of pathogens that could be responsible for diseases for which an infectious cause is suspected. Changing apparent efficacy of vaccines during trials may provide clues to the vaccine's mode of action and/or indicate risk heterogeneity in the trial population. Declining importance of unusual behavioral risk factors may be a signal of increased local transmission of an infection. We review these developments and the related public health implications.
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18
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Kahn R, Hitchings M, Bellan S, Lipsitch M. Impact of stochastically generated heterogeneity in hazard rates on individually randomized vaccine efficacy trials. Clin Trials 2018; 15:207-211. [PMID: 29374974 DOI: 10.1177/1740774517752671] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
Background/aims Network structure and individuals' level of exposure to a pathogen can impact results from efficacy evaluation studies of interventions against infectious diseases. Heterogeneity in infection risk can cause randomized groups to increasingly differ as a trial progresses and as more high-risk individuals become infected (described in prior work as the "frailty" phenomenon). Here, we show the impact this phenomenon can have on an individually randomized trial of a leaky vaccine in which all participants are exchangeable a priori. Methods We model a vaccine trial by generating a network of individuals grouped into communities, which are connected to a larger main population. We then simulate an epidemic, deterministically and with time-varying transmission rates in the main population and stochastically in the communities. The disease natural history follows a susceptible-exposed-infectious-recovered model. Simulation results are used to estimate vaccine efficacy [Formula: see text] with a Cox proportional hazards model. Results We find downward bias in [Formula: see text] associated with low connectivity between communities in the study population and high force of infection, even when all participants in the trial are exchangeable at the time of randomization. This phenomenon arises because the stochastic dynamics in such a setting randomly lead to community-level variation in the force of infection. Stratifying a Cox model by community alleviates this bias with no loss of power. Conclusion Understanding and accounting for the impact of heterogeneous hazard rates can allow for more accurate estimates of [Formula: see text] in epidemic settings.
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Affiliation(s)
- Rebecca Kahn
- 1 Center for Communicable Disease Dynamics, Department of Epidemiology, Harvard T.H. Chan School of Public Health, Boston, MA, USA
| | - Matt Hitchings
- 1 Center for Communicable Disease Dynamics, Department of Epidemiology, Harvard T.H. Chan School of Public Health, Boston, MA, USA
| | - Steven Bellan
- 2 Department of Epidemiology & Biostatistics, College of Public Health, University of Georgia, Athens, GA, USA
| | - Marc Lipsitch
- 1 Center for Communicable Disease Dynamics, Department of Epidemiology, Harvard T.H. Chan School of Public Health, Boston, MA, USA.,3 Department of Immunology and Infectious Diseases, Harvard T.H. Chan School of Public Health, Boston, MA, USA
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19
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Estimating age-time-dependent malaria force of infection accounting for unobserved heterogeneity. Epidemiol Infect 2017; 145:2545-2562. [PMID: 28677517 DOI: 10.1017/s0950268817001297] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Despite well-recognized heterogeneity in malaria transmission, key parameters such as the force of infection (FOI) are generally estimated ignoring the intrinsic variability in individual infection risks. Given the potential impact of heterogeneity on the estimation of the FOI, we estimate this quantity accounting for both observed and unobserved heterogeneity. We used cohort data of children aged 0·5-10 years evaluated for the presence of malaria parasites at three sites in Uganda. Assuming a Susceptible-Infected-Susceptible model, we show how the FOI relates to the point prevalence, enabling the estimation of the FOI by modelling the prevalence using a generalized linear mixed model. We derive bounds for varying parasite clearance distributions. The resulting FOI varies significantly with age and is estimated to be highest among children aged 5-10 years in areas of high and medium malaria transmission and highest in children aged below 1 year in a low transmission setting. Heterogeneity is greater between than within households and it increases with decreasing risk of malaria infection. This suggests that next to the individual's age, heterogeneity in malaria FOI may be attributed to household conditions. When estimating the FOI, accounting for both observed and unobserved heterogeneity in malaria acquisition is important for refining malaria spread models.
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20
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Geographic variation in pneumococcal vaccine efficacy estimated from dynamic modeling of epidemiological data post-PCV7. Sci Rep 2017; 7:3049. [PMID: 28607461 PMCID: PMC5468270 DOI: 10.1038/s41598-017-02955-y] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/24/2016] [Accepted: 04/28/2017] [Indexed: 11/09/2022] Open
Abstract
Although mean efficacy of multivalent pneumococcus vaccines has been intensively studied, variance in vaccine efficacy (VE) has been overlooked. Different net individual protection across settings can be driven by environmental conditions, local serotype and clonal composition, as well as by socio-demographic and genetic host factors. Understanding efficacy variation has implications for population-level effectiveness and other eco-evolutionary feedbacks. Here I show that realized VE can vary across epidemiological settings, by applying a multi-site-one-model approach to data post-vaccination. I analyse serotype prevalence dynamics following PCV7, in asymptomatic carriage in children attending day care in Portugal, Norway, France, Greece, Hungary and Hong-Kong. Model fitting to each dataset provides site-specific estimates for vaccine efficacy against acquisition, and pneumococcal transmission parameters. According to this model, variable serotype replacement across sites can be explained through variable PCV7 efficacy, ranging from 40% in Norway to 10% in Hong-Kong. While the details of how this effect is achieved remain to be determined, here I report three factors negatively associated with the VE readout, including initial prevalence of serotype 19F, daily mean temperature, and the Gini index. The study warrants more attention on local modulators of vaccine performance and calls for predictive frameworks within and across populations.
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21
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McCormick AW, Abuelezam NN, Fussell T, Seage GR, Lipsitch M. Displacement of sexual partnerships in trials of sexual behavior interventions: A model-based assessment of consequences. Epidemics 2017; 20:94-101. [PMID: 28416219 DOI: 10.1016/j.epidem.2017.03.007] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/05/2016] [Revised: 03/30/2017] [Accepted: 03/31/2017] [Indexed: 11/25/2022] Open
Abstract
We investigated the impact of the displacement of sexual activity from adherent recipients of an intervention to others within or outside a trial population on the results from hypothetical trials of different sexual behavior interventions. A short-term model of HIV-prevention interventions that lead to female rejection of male partnership requests showed the impact of displacement expected at the start of a trial. An agent-based model, with sexual mixing and other South African specific demographics, evaluated consequences of displacement for sexual behavior interventions targeting young females in South Africa. This model measured the cumulative incidence among adherent, non-adherent, control and non-enrolled females in a hypothetical trial of HIV prevention. When males made more than one attempt to seek a partnership, interventions reduced short-term HIV infection risk among adherent females, but increased it among non-adherent females as well as controls, non-enrolled (females eligible for the trial but not chosen to participate) and ineligible females (females that did not qualify for the trial due to age). The impact of displacement depends on the intervention and the adherence. In both models, the risk to individuals who are not members of the adherent intervention group will increase with displacement leading to a biased calculation for the effect estimates for the trial. Likewise, intent-to-treat effect estimates become nonlinear functions of the proportion adherent.
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Affiliation(s)
- Alethea W McCormick
- Department of Epidemiology, Harvard T.H. Chan School of Public Health, 677 Huntington Ave, Boston, MA, 02115, USA.
| | - Nadia N Abuelezam
- Department of Epidemiology, Harvard T.H. Chan School of Public Health, 677 Huntington Ave, Boston, MA, 02115, USA; William F. Connell School of Nursing, Boston College, 140 Commonwealth Avenue, Chestnut Hill, MA, 02467, USA
| | - Thomas Fussell
- Department of Epidemiology, Harvard T.H. Chan School of Public Health, 677 Huntington Ave, Boston, MA, 02115, USA
| | - George R Seage
- Department of Epidemiology, Harvard T.H. Chan School of Public Health, 677 Huntington Ave, Boston, MA, 02115, USA
| | - Marc Lipsitch
- Department of Epidemiology, Harvard T.H. Chan School of Public Health, 677 Huntington Ave, Boston, MA, 02115, USA; Center for Communicable Disease Dynamics and Department of Immunology and Infectious Diseases, Harvard T.H. Chan School of Public Health, 677 Huntington Ave, Boston, MA, 02115, USA
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22
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Camacho A, Eggo RM, Goeyvaerts N, Vandebosch A, Mogg R, Funk S, Kucharski AJ, Watson CH, Vangeneugden T, Edmunds WJ. Real-time dynamic modelling for the design of a cluster-randomized phase 3 Ebola vaccine trial in Sierra Leone. Vaccine 2016; 35:544-551. [PMID: 28024952 DOI: 10.1016/j.vaccine.2016.12.019] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/14/2016] [Revised: 11/17/2016] [Accepted: 12/12/2016] [Indexed: 01/03/2023]
Abstract
BACKGROUND Declining incidence and spatial heterogeneity complicated the design of phase 3 Ebola vaccine trials during the tail of the 2013-16 Ebola virus disease (EVD) epidemic in West Africa. Mathematical models can provide forecasts of expected incidence through time and can account for both vaccine efficacy in participants and effectiveness in populations. Determining expected disease incidence was critical to calculating power and determining trial sample size. METHODS In real-time, we fitted, forecasted, and simulated a proposed phase 3 cluster-randomized vaccine trial for a prime-boost EVD vaccine in three candidate regions in Sierra Leone. The aim was to forecast trial feasibility in these areas through time and guide study design planning. RESULTS EVD incidence was highly variable during the epidemic, especially in the declining phase. Delays in trial start date were expected to greatly reduce the ability to discern an effect, particularly as a trial with an effective vaccine would cause the epidemic to go extinct more quickly in the vaccine arm. Real-time updates of the model allowed decision-makers to determine how trial feasibility changed with time. CONCLUSIONS This analysis was useful for vaccine trial planning because we simulated effectiveness as well as efficacy, which is possible with a dynamic transmission model. It contributed to decisions on choice of trial location and feasibility of the trial. Transmission models should be utilised as early as possible in the design process to provide mechanistic estimates of expected incidence, with which decisions about sample size, location, timing, and feasibility can be determined.
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Affiliation(s)
- A Camacho
- Department of Infectious Disease Epidemiology, London School of Hygiene & Tropical Medicine, Keppel Street, London WC1E 7HT, UK
| | - R M Eggo
- Department of Infectious Disease Epidemiology, London School of Hygiene & Tropical Medicine, Keppel Street, London WC1E 7HT, UK.
| | | | | | - R Mogg
- Janssen Research & Development, LLC, Spring House, PA, USA
| | - S Funk
- Department of Infectious Disease Epidemiology, London School of Hygiene & Tropical Medicine, Keppel Street, London WC1E 7HT, UK
| | - A J Kucharski
- Department of Infectious Disease Epidemiology, London School of Hygiene & Tropical Medicine, Keppel Street, London WC1E 7HT, UK
| | - C H Watson
- Department of Infectious Disease Epidemiology, London School of Hygiene & Tropical Medicine, Keppel Street, London WC1E 7HT, UK
| | | | - W J Edmunds
- Department of Infectious Disease Epidemiology, London School of Hygiene & Tropical Medicine, Keppel Street, London WC1E 7HT, UK
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23
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Gomes MGM, Gordon SB, Lalloo DG. Clinical trials: The mathematics of falling vaccine efficacy with rising disease incidence. Vaccine 2016; 34:3007-3009. [PMID: 27177948 PMCID: PMC5087849 DOI: 10.1016/j.vaccine.2016.04.065] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2015] [Revised: 04/15/2016] [Accepted: 04/20/2016] [Indexed: 11/23/2022]
Affiliation(s)
- M Gabriela M Gomes
- Liverpool School of Tropical Medicine, United Kingdom; CIBIO-InBIO, Centro de Investigação em Biodiversidade e Recursos Genéticos, Universidade do Porto, Portugal; Instituto de Matemática e Estatística, Universidade de São Paulo, Brazil.
| | - Stephen B Gordon
- Liverpool School of Tropical Medicine, United Kingdom; Malawi Liverpool Wellcome Trust Programme of Clinical Tropical Research, Blantyre, Malawi
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LEMIEUX-MELLOUKI P, DROLET M, BRISSON J, FRANCO EL, BOILY MC, BAUSSANO I, BRISSON M. Assortative mixing as a source of bias in epidemiological studies of sexually transmitted infections: the case of smoking and human papillomavirus. Epidemiol Infect 2016; 144:1490-9. [PMID: 26584685 PMCID: PMC9150526 DOI: 10.1017/s0950268815002915] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/14/2015] [Revised: 09/23/2015] [Accepted: 10/28/2015] [Indexed: 11/08/2022] Open
Abstract
For studies examining risk factors of sexually transmitted infections (STIs), confounding can stem from characteristics of partners of study subjects, and persist after adjustment for the subjects' individual-level characteristics. Two conditions that can result in confounding by the subjects' partners are: (C1) partner choice is assortative by the risk factor examined and, (C2) sexual activity is associated with the risk factor. The objective of this paper is to illustrate the potential impact of the assortativity bias in studies examining STI risk factors, using smoking and human papillomavirus (HPV) as an example. We developed an HPV transmission-dynamic mathematical model in which we nested a cross-sectional study assessing the smoking-HPV association. In our base case, we assumed (1) no effect of smoking on HPV, and (2) conditions C1-C2 hold for smoking (based on empirical data). The assortativity bias caused an overestimation of the odds ratio (OR) in the simulated study after perfect adjustment for the subjects' individual-level characteristics (adjusted OR 1·51 instead of 1·00). The bias was amplified by a lower basic reproductive number (R 0), greater mixing assortativity and stronger association of smoking with sexual activity. Adjustment for characteristics of partners is needed to mitigate assortativity bias.
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Affiliation(s)
- P. LEMIEUX-MELLOUKI
- CHU de Québec Research Center, Québec, Canada
- Department of Social and Preventive Medicine, Laval University, Québec, Canada
| | - M. DROLET
- CHU de Québec Research Center, Québec, Canada
- Department of Social and Preventive Medicine, Laval University, Québec, Canada
| | - J. BRISSON
- CHU de Québec Research Center, Québec, Canada
- Department of Social and Preventive Medicine, Laval University, Québec, Canada
| | - E. L. FRANCO
- Division of Cancer Epidemiology, McGill University, Montreal, Canada
| | - M.-C. BOILY
- Department of Infectious Disease Epidemiology, Imperial College, London, UK
| | - I. BAUSSANO
- International Agency for Research on Cancer, Lyon, France
| | - M. BRISSON
- CHU de Québec Research Center, Québec, Canada
- Department of Social and Preventive Medicine, Laval University, Québec, Canada
- Department of Infectious Disease Epidemiology, Imperial College, London, UK
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Immunogenicity of the RTS,S/AS01 malaria vaccine and implications for duration of vaccine efficacy: secondary analysis of data from a phase 3 randomised controlled trial. THE LANCET. INFECTIOUS DISEASES 2015; 15:1450-8. [PMID: 26342424 PMCID: PMC4655306 DOI: 10.1016/s1473-3099(15)00239-x] [Citation(s) in RCA: 219] [Impact Index Per Article: 24.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 06/05/2015] [Revised: 07/16/2015] [Accepted: 07/22/2015] [Indexed: 02/02/2023]
Abstract
BACKGROUND The RTS,S/AS01 malaria vaccine targets the circumsporozoite protein, inducing antibodies associated with the prevention of Plasmodium falciparum infection. We assessed the association between anti-circumsporozoite antibody titres and the magnitude and duration of vaccine efficacy using data from a phase 3 trial done between 2009 and 2014. METHODS Using data from 8922 African children aged 5-17 months and 6537 African infants aged 6-12 weeks at first vaccination, we analysed the determinants of immunogenicity after RTS,S/AS01 vaccination with or without a booster dose. We assessed the association between the incidence of clinical malaria and anti-circumsporozoite antibody titres using a model of anti-circumsporozoite antibody dynamics and the natural acquisition of protective immunity over time. FINDINGS RTS,S/AS01-induced anti-circumsporozoite antibody titres were greater in children aged 5-17 months than in those aged 6-12 weeks. Pre-vaccination anti-circumsporozoite titres were associated with lower immunogenicity in children aged 6-12 weeks and higher immunogenicity in those aged 5-17 months. The immunogenicity of the booster dose was strongly associated with immunogenicity after primary vaccination. Anti-circumsporozoite titres wane according to a biphasic exponential distribution. In participants aged 5-17 months, the half-life of the short-lived component of the antibody response was 45 days (95% credible interval 42-48) and that of the long-lived component was 591 days (557-632). After primary vaccination 12% (11-13) of the response was estimated to be long-lived, rising to 30% (28-32%) after a booster dose. An anti-circumsporozoite antibody titre of 121 EU/mL (98-153) was estimated to prevent 50% of infections. Waning anti-circumsporozoite antibody titres predict the duration of efficacy against clinical malaria across different age categories and transmission intensities, and efficacy wanes more rapidly at higher transmission intensity. INTERPRETATION Anti-circumsporozoite antibody titres are a surrogate of protection for the magnitude and duration of RTS,S/AS01 efficacy, with or without a booster dose, providing a valuable surrogate of effectiveness for new RTS,S formulations in the age groups considered. FUNDING UK Medical Research Council.
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Metzger WG, Köhler C, Mordmüller B. Lessons from a modern review of the smallpox eradication files. J R Soc Med 2015; 108:473-7. [PMID: 26432815 PMCID: PMC4698834 DOI: 10.1177/0141076815605211] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022] Open
Affiliation(s)
- Wolfram G Metzger
- Institute of Tropical Medicine, Eberhard Karls University, Tübingen 72074, Germany
| | - Carsten Köhler
- Institute of Tropical Medicine, Eberhard Karls University, Tübingen 72074, Germany
| | - Benjamin Mordmüller
- Institute of Tropical Medicine, Eberhard Karls University, Tübingen 72074, Germany
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McCarthy KA, Wenger EA, Huynh GH, Eckhoff PA. Calibration of an intrahost malaria model and parameter ensemble evaluation of a pre-erythrocytic vaccine. Malar J 2015; 14:6. [PMID: 25563798 PMCID: PMC4326442 DOI: 10.1186/1475-2875-14-6] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/26/2014] [Accepted: 12/16/2014] [Indexed: 01/10/2023] Open
Abstract
Background A pre-erythrocytic vaccine could provide a useful tool for burden reduction and eventual eradication of malaria. Mathematical malaria models provide a mechanism for evaluating the effective burden reduction across a range of transmission conditions where such a vaccine might be deployed. Methods The EMOD model is an individual-based model of malaria transmission dynamics, including vector lifecycles and species-specific behaviour, coupled to a mechanistic intrahost model of malaria parasite and host immune system dynamics. The present work describes the extension of the EMOD model to include diagnoses of severe malaria and iterative calibration of the immune system parameters and parasite antigenic variation to age-stratified prevalence, incidence and severe disease incidence data obtained from multiple regions with broadly varying transmission conditions in Africa. An ensemble of calibrated model parameter sets is then employed to evaluate the potential impact of routine immunization with a pre-erythrocytic vaccine. Results The reduction in severe malaria burden exhibits a broad peak at moderate transmission conditions. Under sufficiently intense transmission, a vaccine that reduces but does not eliminate the probability of acquisition from a single challenge bite may delay infections but produces minimal or no net reduction. Conversely, under sufficiently weak transmission conditions, a vaccine can provide a high fractional reduction but avert a relatively low absolute number of cases due to low baseline burden. Conclusions Roll-out of routine immunization with pre-erythrocytic malaria vaccines can provide substantial burden reduction across a range of transmission conditions typical to many regions in Africa. Electronic supplementary material The online version of this article (doi:10.1186/1475-2875-14-6) contains supplementary material, which is available to authorized users.
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Affiliation(s)
- Kevin A McCarthy
- Institute for Disease Modeling, 1555 132nd Ave NE, Bellevue, WA 98005, USA.
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Magpantay FMG, Riolo MA, DE Cellès MD, King AA, Rohani P. EPIDEMIOLOGICAL CONSEQUENCES OF IMPERFECT VACCINES FOR IMMUNIZING INFECTIONS. SIAM JOURNAL ON APPLIED MATHEMATICS 2014; 74:1810-1830. [PMID: 25878365 PMCID: PMC4394665 DOI: 10.1137/140956695] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/13/2023]
Abstract
The control of some childhood diseases has proven to be difficult even in countries that maintain high vaccination coverage. This may be due to the use of imperfect vaccines and there has been much discussion on the different modes by which vaccines might fail. To understand the epidemiological implications of some of these different modes, we performed a systematic analysis of a model based on the standard SIR equations with a vaccinated component that permits vaccine failure in degree ("leakiness"), take ("all-or-nothingness") and duration (waning of vaccine-derived immunity). The model was first considered as a system of ordinary differential equations, then extended to a system of partial differential equations to accommodate age structure. We derived analytic expressions for the steady states of the system and the final age distributions in the case of homogenous contact rates. The stability of these equilibria are determined by a threshold parameter Rp , a function of the vaccine failure parameters and the coverage p. The value of p for which Rp = 1 yields the critical vaccination ratio, a measure of herd immunity. Using this concept we can compare vaccines that confer the same level of herd immunity to the population but may fail at the individual level in different ways. For any fixed Rp > 1, the leaky model results in the highest prevalence of infection, while the all-or-nothing and waning models have the same steady state prevalence. The actual composition of a vaccine cannot be determined on the basis of steady state levels alone, however the distinctions can be made by looking at transient dynamics (such as after the onset of vaccination), the mean age of infection, the age distributions at steady state of the infected class, and the effect of age-specific contact rates.
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Affiliation(s)
- F M G Magpantay
- Department of Ecology and Evolutionary Biology, University of Michigan, Ann Arbor, MI 48109, USA
| | - M A Riolo
- Department of Mathematics, University of Michigan, Ann Arbor, MI 48109, USA
| | - M Domenech DE Cellès
- Department of Ecology and Evolutionary Biology, University of Michigan, Ann Arbor, MI 48109, USA
| | - A A King
- Department of Ecology and Evolutionary Biology, University of Michigan, Ann Arbor, MI 48109, USA ; Department of Mathematics, University of Michigan, Ann Arbor, MI 48109, USA ; Fogarty International Center, National Institutes of Health, Bethesda, MD 20892, USA
| | - P Rohani
- Department of Ecology and Evolutionary Biology, University of Michigan, Ann Arbor, MI 48109, USA ; Center for the Study of Complex Systems, University of Michigan, Ann Arbor, MI 48109, USA ; Fogarty International Center, National Institutes of Health, Bethesda, MD 20892, USA
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Stevenson JC, Stresman GH, Gitonga CW, Gillig J, Owaga C, Marube E, Odongo W, Okoth A, China P, Oriango R, Brooker SJ, Bousema T, Drakeley C, Cox J. Reliability of school surveys in estimating geographic variation in malaria transmission in the western Kenyan highlands. PLoS One 2013; 8:e77641. [PMID: 24143250 PMCID: PMC3797060 DOI: 10.1371/journal.pone.0077641] [Citation(s) in RCA: 40] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2013] [Accepted: 09/12/2013] [Indexed: 11/25/2022] Open
Abstract
Background School surveys provide an operational approach to assess malaria transmission through parasite prevalence. There is limited evidence on the comparability of prevalence estimates obtained from school and community surveys carried out at the same locality. Methods Concurrent school and community cross-sectional surveys were conducted in 46 school/community clusters in the western Kenyan highlands and households of school children were geolocated. Malaria was assessed by rapid diagnostic test (RDT) and combined seroprevalence of antibodies to bloodstage Plasmodium falciparum antigens. Results RDT prevalence in school and community populations was 25.7% (95% CI: 24.4-26.8) and 15.5% (95% CI: 14.4-16.7), respectively. Seroprevalence in the school and community populations was 51.9% (95% CI: 50.5-53.3) and 51.5% (95% CI: 49.5-52.9), respectively. RDT prevalence in schools could differentiate between low (<7%, 95% CI: 0-19%) and high (>39%, 95% CI: 25-49%) transmission areas in the community and, after a simple adjustment, were concordant with the community estimates. Conclusions Estimates of malaria prevalence from school surveys were consistently higher than those from community surveys and were strongly correlated. School-based estimates can be used as a reliable indicator of malaria transmission intensity in the wider community and may provide a basis for identifying priority areas for malaria control.
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Affiliation(s)
- Jennifer C. Stevenson
- Department of Disease Control, London School of Hygiene & Tropical Medicine, London, United Kingdom
| | - Gillian H. Stresman
- Department of Immunology and Infection, London School of Hygiene & Tropical Medicine, London, United Kingdom
| | - Caroline W. Gitonga
- Department of Disease Control, London School of Hygiene & Tropical Medicine, London, United Kingdom
- Malaria Public Health Department, Kenya Medical Research Institute/Wellcome Trust Research Programme, Nairobi, Kenya
| | - Jonathan Gillig
- Eck Institute for Global Health, University of Notre Dame, South Bend, Indiana, United States of America
| | - Chrispin Owaga
- Center for Global Health Research, Kenya Medical Research Institute/Centers for Disease Control and Prevention, Kisumu, Kenya
| | - Elizabeth Marube
- Center for Global Health Research, Kenya Medical Research Institute/Centers for Disease Control and Prevention, Kisumu, Kenya
| | - Wycliffe Odongo
- Center for Global Health Research, Kenya Medical Research Institute/Centers for Disease Control and Prevention, Kisumu, Kenya
| | - Albert Okoth
- Center for Global Health Research, Kenya Medical Research Institute/Centers for Disease Control and Prevention, Kisumu, Kenya
| | - Pauline China
- Center for Global Health Research, Kenya Medical Research Institute/Centers for Disease Control and Prevention, Kisumu, Kenya
| | - Robin Oriango
- Center for Global Health Research, Kenya Medical Research Institute/Centers for Disease Control and Prevention, Kisumu, Kenya
| | - Simon J. Brooker
- Department of Disease Control, London School of Hygiene & Tropical Medicine, London, United Kingdom
- Malaria Public Health Department, Kenya Medical Research Institute/Wellcome Trust Research Programme, Nairobi, Kenya
| | - Teun Bousema
- Department of Immunology and Infection, London School of Hygiene & Tropical Medicine, London, United Kingdom
- Department of Medical Microbiology, Radboud University Nijmegen Medical Centre, Nijmegen, The Netherlands
| | - Chris Drakeley
- Department of Immunology and Infection, London School of Hygiene & Tropical Medicine, London, United Kingdom
| | - Jonathan Cox
- Department of Disease Control, London School of Hygiene & Tropical Medicine, London, United Kingdom
- * E-mail:
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Cairns ME, Asante KP, Owusu-Agyei S, Chandramohan D, Greenwood BM, Milligan PJ. Analysis of partial and complete protection in malaria cohort studies. Malar J 2013; 12:355. [PMID: 24093726 PMCID: PMC3850882 DOI: 10.1186/1475-2875-12-355] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/03/2013] [Accepted: 10/02/2013] [Indexed: 11/15/2022] Open
Abstract
Background Malaria transmission is highly heterogeneous and analysis of incidence data must account for this for correct statistical inference. Less widely appreciated is the occurrence of a large number of zero counts (children without a malaria episode) in malaria cohort studies. Zero-inflated regression methods provide one means of addressing this issue, and also allow risk factors providing complete and partial protection to be disentangled. Methods Poisson, negative binomial (NB), zero-inflated Poisson (ZIP) and zero-inflated negative binomial (ZINB) regression models were fitted to data from two cohort studies of malaria in children in Ghana. Multivariate models were used to understand risk factors for elevated incidence of malaria and for remaining malaria-free, and to estimate the fraction of the population not at risk of malaria. Results ZINB models, which account for both heterogeneity in individual risk and an unexposed sub-group within the population, provided the best fit to data in both cohorts. These approaches gave additional insight into the mechanism of factors influencing the incidence of malaria compared to simpler approaches, such as NB regression. For example, compared to urban areas, rural residence was found to both increase the incidence rate of malaria among exposed children, and increase the probability of being exposed. In Navrongo, 34% of urban residents were estimated to be at no risk, compared to 3% of rural residents. In Kintampo, 47% of urban residents and 13% of rural residents were estimated to be at no risk. Conclusion These results illustrate the utility of zero-inflated regression methods for analysis of malaria cohort data that include a large number of zero counts. Specifically, these results suggest that interventions that reach mainly urban residents will have limited overall impact, since some urban residents are essentially at no risk, even in areas of high endemicity, such as in Ghana.
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Affiliation(s)
- Matthew E Cairns
- MRC Tropical Epidemiology Group, London School of Hygiene & Tropical Medicine, London, UK.
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Stuckey EM, Smith TA, Chitnis N. Estimating malaria transmission through mathematical models. Trends Parasitol 2013; 29:477-82. [PMID: 24001452 DOI: 10.1016/j.pt.2013.08.001] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/30/2013] [Revised: 08/02/2013] [Accepted: 08/05/2013] [Indexed: 10/26/2022]
Abstract
Evaluating the effectiveness of malaria control interventions on the basis of their impact on transmission is increasingly important as countries move from malaria control to pre-elimination programs. Mathematical modeling can examine relationships between malaria indicators, allowing translation of easily measured data into measures of transmission, and addressing key concerns with traditional methods for quantifying transmission. Simulations show these indicators are statistically correlated, allowing direct comparisons of malaria transmission using data collected using different methods across a range of transmission intensities and seasonal patterns. Results from such models can provide public health officials with accurate estimates of transmission, by seasonal pattern, that are necessary for assessing and tailoring malaria control and elimination programs to specific settings.
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Affiliation(s)
- Erin M Stuckey
- Department of Epidemiology and Public Health, Swiss Tropical and Public Health Institute, Socinstrasse 57, Postfach, 4002 Basel, Switzerland; University of Basel, Petersplatz 1, 4003 Basel, Switzerland.
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White MT, Griffin JT, Ghani AC. The design and statistical power of treatment re-infection studies of the association between pre-erythrocytic immunity and infection with Plasmodium falciparum. Malar J 2013; 12:278. [PMID: 23927576 PMCID: PMC3751675 DOI: 10.1186/1475-2875-12-278] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/09/2013] [Accepted: 07/01/2013] [Indexed: 11/30/2022] Open
Abstract
Background Understanding the role of pre-erythrocytic immune responses to Plasmodium falciparum parasites is crucial for understanding the epidemiology of malaria. However, published studies have reported inconsistent results on the association between markers of pre-erythrocytic immunity and protection from malaria. Methods The design and statistical methods of studies of pre-erythrocytic immunity were reviewed, and factors affecting the likelihood of detecting statistically significant associations were assessed. Treatment re-infection studies were simulated to estimate the effects of study size, transmission intensity, and sampling frequency on the statistical power to detect an association between markers of pre-erythrocytic immunity and protection from infection. Results Nine of nineteen studies reviewed reported statistically significant associations between markers of pre-erythrocytic immunity and protection from infection. Studies with large numbers of participants in high-transmission settings, followed longitudinally with active detection of infection and with immune responses analysed as continuous variables, were most likely to detect statistically significant associations. Simulation of treatment re-infection studies highlights that many studies are underpowered to detect statistically significant associations, providing an explanation for the finding that only some studies report significant associations between pre-erythrocytic immune responses and protection from infection. Conclusions The findings of the review and model simulations are consistent with the hypothesis that pre-erythrocytic immune responses prevent P. falciparum infections, but that many studies are underpowered to consistently detect this effect.
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Affiliation(s)
- Michael T White
- MRC Centre for Outbreak Analysis and Modelling, Department of Infectious Disease Epidemiology, Imperial College London, Norfolk Place, London, UK.
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White MT, Bejon P, Olotu A, Griffin JT, Riley EM, Kester KE, Ockenhouse CF, Ghani AC. The relationship between RTS,S vaccine-induced antibodies, CD4⁺ T cell responses and protection against Plasmodium falciparum infection. PLoS One 2013; 8:e61395. [PMID: 23613845 PMCID: PMC3628884 DOI: 10.1371/journal.pone.0061395] [Citation(s) in RCA: 135] [Impact Index Per Article: 12.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/21/2012] [Accepted: 03/08/2013] [Indexed: 01/09/2023] Open
Abstract
Vaccination with the pre-erythrocytic malaria vaccine RTS,S induces high levels of antibodies and CD4+ T cells specific for the circumsporozoite protein (CSP). Using a biologically-motivated mathematical model of sporozoite infection fitted to data from malaria-naive adults vaccinated with RTS,S and subjected to experimental P. falciparum challenge, we characterised the relationship between antibodies, CD4+ T cell responses and protection from infection. Both anti-CSP antibody titres and CSP-specific CD4+ T cells were identified as immunological surrogates of protection, with RTS,S induced anti-CSP antibodies estimated to prevent 32% (95% confidence interval (CI) 24%–41%) of infections. The addition of RTS,S-induced CSP-specific CD4+ T cells was estimated to increase vaccine efficacy against infection to 40% (95% CI, 34%–48%). This protective efficacy is estimated to result from a 96.1% (95% CI, 93.4%–97.8%) reduction in the liver-to-blood parasite inoculum, indicating that in volunteers who developed P. falciparum infection, a small number of parasites (often the progeny of a single surviving sporozoite) are responsible for breakthrough blood-stage infections.
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Affiliation(s)
- Michael T White
- MRC Centre for Outbreak Analysis and Modelling, Department of Infectious Disease Epidemiology, Imperial College London, London, United Kingdom.
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Wenger EA, Eckhoff PA. A mathematical model of the impact of present and future malaria vaccines. Malar J 2013; 12:126. [PMID: 23587051 PMCID: PMC3658952 DOI: 10.1186/1475-2875-12-126] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/13/2012] [Accepted: 03/20/2013] [Indexed: 11/30/2022] Open
Abstract
Background With the encouraging advent of new malaria vaccine candidates, mathematical modelling of expected impacts of present and future vaccines as part of multi-intervention strategies is especially relevant. Methods The impact of potential malaria vaccines is presented utilizing the EMOD model, a comprehensive model of the vector life cycle coupled to a detailed mechanistic representation of intra-host parasite and immune dynamics. Values of baseline transmission and vector feeding behaviour parameters are identified, for which local elimination is enabled by layering pre-erythrocytic vaccines of various efficacies on top of high and sustained insecticide-treated net coverage. The expected reduction in clinical cases is further explored in a scenario that targets children by adding a pre-erythrocytic vaccine to the EPI programme for newborns. Results At high transmission, there is a minimal reduction in clinical disease cases, as the time to infection is only slightly delayed. At lower transmission, there is an accelerating community-level protection that has subtle dependences on heterogeneities in vector behaviour, ecology, and intervention coverage. At very low transmission, the trend reverses as many children are vaccinated to prevent few cases. Conclusions The maximum-impact setting is one in which the impact of increasing bed net coverage has saturated, vector feeding is primarily outdoors, and transmission is just above the threshold where small perturbations from a vaccine intervention result in large community benefits.
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Olotu A, Fegan G, Wambua J, Nyangweso G, Awuondo KO, Leach A, Lievens M, Leboulleux D, Njuguna P, Peshu N, Marsh K, Bejon P. Four-year efficacy of RTS,S/AS01E and its interaction with malaria exposure. N Engl J Med 2013; 368:1111-20. [PMID: 23514288 PMCID: PMC5156295 DOI: 10.1056/nejmoa1207564] [Citation(s) in RCA: 197] [Impact Index Per Article: 17.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
BACKGROUND The candidate malaria vaccine RTS,S/AS01E has entered phase 3 trials, but data on long-term outcomes are limited. METHODS For 4 years, we followed children who had been randomly assigned, at 5 to 17 months of age, to receive three doses of RTS,S/AS01E vaccine (223 children) or rabies vaccine (224 controls). The end point was clinical malaria (temperature of ≥37.5°C and Plasmodium falciparum parasitemia density of >2500 parasites per cubic millimeter). Each child's exposure to malaria was estimated with the use of the distance-weighted local prevalence of malaria. RESULTS Over a period of 4 years, 118 of 223 children who received the RTS,S/AS01E vaccine and 138 of 224 of the controls had at least 1 episode of clinical malaria. Vaccine efficacies in the intention-to-treat and per-protocol analyses were 29.9% (95% confidence interval [CI], 10.3 to 45.3; P=0.005) and 32.1% (95% CI, 11.6 to 47.8; P=0.004), respectively, calculated by Cox regression. Multiple episodes were common, with 551 and 618 malarial episodes in the RTS,S/AS01E and control groups, respectively; vaccine efficacies in the intention-to-treat and per-protocol analyses were 16.8% (95% CI, -8.6 to 36.3; P=0.18) and 24.3% (95% CI, 1.9 to 41.6; P=0.04), respectively, calculated by the Andersen-Gill extension of the Cox model. For every 100 vaccinated children, 65 cases of clinical malaria were averted. Vaccine efficacy declined over time (P=0.004) and with increasing exposure to malaria (P=0.001) in the per-protocol analysis. Vaccine efficacy was 43.6% (95% CI, 15.5 to 62.3) in the first year but was -0.4% (95% CI, -32.1 to 45.3) in the fourth year. Among children with a malaria-exposure index that was average or lower than average, the vaccine efficacy was 45.1% (95% CI, 11.3 to 66.0), but among children with a malaria-exposure index that was higher than average it was 15.9% (95% CI, -11.0 to 36.4). CONCLUSIONS The efficacy of RTS,S/AS01E vaccine over the 4-year period was 16.8%. Efficacy declined over time and with increasing malaria exposure. (Funded by the PATH Malaria Vaccine Initiative and Wellcome Trust; ClinicalTrials.gov number, NCT00872963.).
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Affiliation(s)
- Ally Olotu
- Centre for Geographic Medicine Research, Kenya Medical Research Institute (KEMRI)-Wellcome Trust Research Programme, Kilifi, Kenya.
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Bejon P, White MT, Olotu A, Bojang K, Lusingu JPA, Salim N, Otsyula NN, Agnandji ST, Asante KP, Owusu-Agyei S, Abdulla S, Ghani AC. Efficacy of RTS,S malaria vaccines: individual-participant pooled analysis of phase 2 data. THE LANCET. INFECTIOUS DISEASES 2013; 13:319-27. [PMID: 23454164 PMCID: PMC3771416 DOI: 10.1016/s1473-3099(13)70005-7] [Citation(s) in RCA: 69] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
Background The efficacy of RTS,S/AS01 as a vaccine for malaria is being tested in a phase 3 clinical trial. Early results show significant, albeit partial, protection against clinical malaria and severe malaria. To ascertain variations in vaccine efficacy according to covariates such as transmission intensity, choice of adjuvant, age at vaccination, and bednet use, we did an individual-participant pooled analysis of phase 2 clinical data. Methods We analysed data from 11 different sites in Africa, including 4453 participants. We measured heterogeneity in vaccine efficacy by estimating the interactions between covariates and vaccination in pooled multivariable Cox regression and Poisson regression analyses. Endpoints for measurement of vaccine efficacy were infection, clinical malaria, severe malaria, and death. We defined transmission intensity levels according to the estimated local parasite prevalence in children aged 2–10 years (PrP2–10), ranging from 5% to 80%. Choice of adjuvant was either AS01 or AS02. Findings Vaccine efficacy against all episodes of clinical malaria varied by transmission intensity (p=0·001). At low transmission (PrP2–10 10%) vaccine efficacy was 60% (95% CI 54 to 67), at moderate transmission (PrP2–10 20%) it was 41% (21 to 57), and at high transmission (PrP2–10 70%) the efficacy was 4% (−10 to 22). Vaccine efficacy also varied by adjuvant choice (p<0·0001)—eg, at low transmission (PrP2–10 10%), efficacy varied from 60% (95% CI 54 to 67) for AS01 to 47% (14 to 75) for AS02. Variations in efficacy by age at vaccination were of borderline significance (p=0·038), and bednet use and sex were not significant covariates. Vaccine efficacy (pooled across adjuvant choice and transmission intensity) varied significantly (p<0·0001) according to time since vaccination, from 36% efficacy (95% CI 24 to 45) at time of vaccination to 0% (−38 to 38) after 3 years. Interpretation Vaccine efficacy against clinical disease was of limited duration and was not detectable 3 years after vaccination. Furthermore, efficacy fell with increasing transmission intensity. Outcomes after vaccination cannot be gauged accurately on the basis of one pooled efficacy figure. However, predictions of public-health outcomes of vaccination will need to take account of variations in efficacy by transmission intensity and by time since vaccination. Funding Medical Research Council (UK); Bill & Melinda Gates Foundation Vaccine Modelling Initiative; Wellcome Trust.
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Affiliation(s)
- Philip Bejon
- KEMRI-Wellcome Trust Research Programme, Kenya Medical Research Institute, Kilifi, Kenya.
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Abdulla S, Salim N, Machera F, Kamata R, Juma O, Shomari M, Kubhoja S, Mohammed A, Mwangoka G, Aebi T, Mshinda H, Schellenberg D, Carter T, Villafana T, Dubois MC, Leach A, Lievens M, Vekemans J, Cohen J, Ballou WR, Tanner M. Randomized, controlled trial of the long term safety, immunogenicity and efficacy of RTS,S/AS02(D) malaria vaccine in infants living in a malaria-endemic region. Malar J 2013; 12:11. [PMID: 23297680 PMCID: PMC3557164 DOI: 10.1186/1475-2875-12-11] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/07/2012] [Accepted: 01/04/2013] [Indexed: 12/16/2022] Open
Abstract
BACKGROUND The RTS,S/AS malaria candidate vaccine is being developed with the intent to be delivered, if approved, through the Expanded Programme on Immunization (EPI) of the World Health Organization. Safety, immunogenicity and efficacy of the RTS,S/AS02(D) vaccine candidate when integrated into a standard EPI schedule for infants have been reported over a nine-month surveillance period. This paper describes results following 20 months of follow up. METHODS This Phase IIb, single-centre, randomized controlled trial enrolled 340 infants in Tanzania to receive three doses of RTS,S/AS02(D) or hepatitis B vaccine at 8, 12, and 16 weeks of age. All infants also received DTPw/Hib (diphtheria and tetanus toxoids, whole-cell pertussis vaccine, conjugated Haemophilus influenzae type b vaccine) at the same timepoints. The study was double-blinded to month 9 and single-blinded from months 9 to 20. RESULTS From month 0 to 20, at least one SAE was reported in 57/170 infants who received RTS,S/AS02(D) (33.5%; 95% confidence interval [CI]: 26.5, 41.2) and 62/170 infants who received hepatitis B vaccine (36.5%; 95% CI: 29.2, 44.2). The SAE profile was similar in both vaccine groups; none were considered to be related to vaccination. At month 20, 18 months after completion of vaccination, 71.8% of recipients of RTS,S/AS02(D) and 3.8% of recipients of hepatitis B vaccine had seropositive titres for anti-CS antibodies; seroprotective levels of anti-HBs antibodies remained in 100% of recipients of RTS,S/AS02(D) and 97.7% recipients of hepatitis B vaccine. Anti-HBs antibody GMTs were higher in the RTS,S/AS02(D) group at all post-vaccination time points compared to control. According to protocol population, vaccine efficacy against multiple episodes of malaria disease was 50.7% (95% CI: -6.5 to 77.1, p = 0.072) and 26.7% (95% CI: -33.1 to 59.6, p = 0.307) over 12 and 18 months post vaccination, respectively. In the Intention to Treat population, over the 20-month follow up, vaccine efficacy against multiple episodes of malaria disease was 14.4% (95% CI: -41.9 to 48.4, p = 0.545). CONCLUSIONS The acceptable safety profile and good tolerability of RTS,S/AS02(D) in combination with EPI vaccines previously reported from month 0 to 9 was confirmed over a 20 month surveillance period in this infant population. Antibodies against both CS and HBsAg in the RTS,S/AS02(D) group remained significantly higher compared to control for the study duration. Over 18 months follow up, RTS,S/AS02(D) prevented approximately a quarter of malaria cases in the study population. CLINICAL TRIALS Gov identifier: NCT00289185.
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Affiliation(s)
- Salim Abdulla
- Bagamoyo Research and Training Centre of Ifakara Health Institute, Pwani, Tanzania
- Ifakara Health Institute, 360 Kiko Avenue, Mikocheni, PO Box 78373, Dar es Salaam, Tanzania
| | - Nahya Salim
- Bagamoyo Research and Training Centre of Ifakara Health Institute, Pwani, Tanzania
| | - Francisca Machera
- Bagamoyo Research and Training Centre of Ifakara Health Institute, Pwani, Tanzania
| | - Richard Kamata
- Bagamoyo Research and Training Centre of Ifakara Health Institute, Pwani, Tanzania
| | - Omar Juma
- Bagamoyo Research and Training Centre of Ifakara Health Institute, Pwani, Tanzania
| | - Mwanajaa Shomari
- Bagamoyo Research and Training Centre of Ifakara Health Institute, Pwani, Tanzania
| | - Sulende Kubhoja
- Muhimbili University of Health and Allied Sciences, Dar es Salaam, Tanzania
| | - Ali Mohammed
- Bagamoyo Research and Training Centre of Ifakara Health Institute, Pwani, Tanzania
| | - Grace Mwangoka
- Bagamoyo Research and Training Centre of Ifakara Health Institute, Pwani, Tanzania
| | - Thomas Aebi
- Bagamoyo Research and Training Centre of Ifakara Health Institute, Pwani, Tanzania
- Swiss Tropical and Public Health Institute, Basel, Switzerland
| | - Hassan Mshinda
- Tanzania Commission for Science and Technology, Dar es Salaam, Tanzania
| | | | | | | | | | - Amanda Leach
- GlaxoSmithKline Biologicals, Rue De L'Institut 89, Rixensart, Belgium
| | - Marc Lievens
- GlaxoSmithKline Biologicals, Rue De L'Institut 89, Rixensart, Belgium
| | - Johan Vekemans
- GlaxoSmithKline Biologicals, Rue De L'Institut 89, Rixensart, Belgium
| | - Joe Cohen
- GlaxoSmithKline Biologicals, Rue De L'Institut 89, Rixensart, Belgium
| | - W Ripley Ballou
- GlaxoSmithKline Biologicals, Rue De L'Institut 89, Rixensart, Belgium
| | - Marcel Tanner
- Swiss Tropical and Public Health Institute, Basel, Switzerland
- University of Basel, Basel, Switzerland
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Agnandji ST, Lell B, Fernandes JF, Abossolo BP, Methogo BGNO, Kabwende AL, Adegnika AA, Mordmüller B, Issifou S, Kremsner PG, Sacarlal J, Aide P, Lanaspa M, Aponte JJ, Machevo S, Acacio S, Bulo H, Sigauque B, Macete E, Alonso P, Abdulla S, Salim N, Minja R, Mpina M, Ahmed S, Ali AM, Mtoro AT, Hamad AS, Mutani P, Tanner M, Tinto H, D'Alessandro U, Sorgho H, Valea I, Bihoun B, Guiraud I, Kaboré B, Sombié O, Guiguemdé RT, Ouédraogo JB, Hamel MJ, Kariuki S, Oneko M, Odero C, Otieno K, Awino N, McMorrow M, Muturi-Kioi V, Laserson KF, Slutsker L, Otieno W, Otieno L, Otsyula N, Gondi S, Otieno A, Owira V, Oguk E, Odongo G, Woods JB, Ogutu B, Njuguna P, Chilengi R, Akoo P, Kerubo C, Maingi C, Lang T, Olotu A, Bejon P, Marsh K, Mwambingu G, Owusu-Agyei S, Asante KP, Osei-Kwakye K, Boahen O, Dosoo D, Asante I, Adjei G, Kwara E, Chandramohan D, Greenwood B, Lusingu J, Gesase S, Malabeja A, Abdul O, Mahende C, Liheluka E, Malle L, Lemnge M, Theander TG, Drakeley C, Ansong D, Agbenyega T, Adjei S, Boateng HO, Rettig T, Bawa J, Sylverken J, Sambian D, Sarfo A, Agyekum A, Martinson F, Hoffman I, Mvalo T, Kamthunzi P, Nkomo R, Tembo T, Tegha G, Tsidya M, Kilembe J, Chawinga C, Ballou WR, Cohen J, Guerra Y, Jongert E, Lapierre D, Leach A, Lievens M, Ofori-Anyinam O, Olivier A, Vekemans J, Carter T, Kaslow D, Leboulleux D, Loucq C, Radford A, Savarese B, Schellenberg D, Sillman M, Vansadia P. A phase 3 trial of RTS,S/AS01 malaria vaccine in African infants. N Engl J Med 2012; 367:2284-95. [PMID: 23136909 PMCID: PMC10915853 DOI: 10.1056/nejmoa1208394] [Citation(s) in RCA: 541] [Impact Index Per Article: 45.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
BACKGROUND The candidate malaria vaccine RTS,S/AS01 reduced episodes of both clinical and severe malaria in children 5 to 17 months of age by approximately 50% in an ongoing phase 3 trial. We studied infants 6 to 12 weeks of age recruited for the same trial. METHODS We administered RTS,S/AS01 or a comparator vaccine to 6537 infants who were 6 to 12 weeks of age at the time of the first vaccination in conjunction with Expanded Program on Immunization (EPI) vaccines in a three-dose monthly schedule. Vaccine efficacy against the first or only episode of clinical malaria during the 12 months after vaccination, a coprimary end point, was analyzed with the use of Cox regression. Vaccine efficacy against all malaria episodes, vaccine efficacy against severe malaria, safety, and immunogenicity were also assessed. RESULTS The incidence of the first or only episode of clinical malaria in the intention-to-treat population during the 14 months after the first dose of vaccine was 0.31 per person-year in the RTS,S/AS01 group and 0.40 per person-year in the control group, for a vaccine efficacy of 30.1% (95% confidence interval [CI], 23.6 to 36.1). Vaccine efficacy in the per-protocol population was 31.3% (97.5% CI, 23.6 to 38.3). Vaccine efficacy against severe malaria was 26.0% (95% CI, -7.4 to 48.6) in the intention-to-treat population and 36.6% (95% CI, 4.6 to 57.7) in the per-protocol population. Serious adverse events occurred with a similar frequency in the two study groups. One month after administration of the third dose of RTS,S/AS01, 99.7% of children were positive for anti-circumsporozoite antibodies, with a geometric mean titer of 209 EU per milliliter (95% CI, 197 to 222). CONCLUSIONS The RTS,S/AS01 vaccine coadministered with EPI vaccines provided modest protection against both clinical and severe malaria in young infants. (Funded by GlaxoSmithKline Biologicals and the PATH Malaria Vaccine Initiative; RTS,S ClinicalTrials.gov number, NCT00866619.).
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Distinguishing vaccine efficacy and effectiveness. Vaccine 2012; 30:6700-5. [PMID: 22944629 DOI: 10.1016/j.vaccine.2012.08.045] [Citation(s) in RCA: 47] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/24/2012] [Revised: 08/03/2012] [Accepted: 08/18/2012] [Indexed: 11/23/2022]
Abstract
BACKGROUND Mathematical models of disease transmission and vaccination typically assume that protective vaccine efficacy (i.e. the relative reduction in the transmission rate among vaccinated individuals) is equivalent to direct effectiveness of vaccine. This assumption has not been evaluated. METHODS We used dynamic epidemiological models of influenza and measles vaccines to evaluate the common measures of vaccine effectiveness in terms of both the protection of individuals and disease control within populations. We determined how vaccine-mediated reductions in attack rates translate into vaccine efficacy as well as into the common population measures of 'direct', 'indirect', 'total', and 'overall' effects of vaccination with examples of compartmental models of influenza and measles vaccination. RESULTS We found that the typical parameterization of vaccine efficacy using direct effectiveness of vaccine can lead to the underestimation of the impact of vaccine. Such underestimation occurs when the vaccine is assumed to offer partial protection to every vaccinated person, and becomes worse when the level of vaccine coverage is low. Nevertheless, estimates of 'total', 'indirect' and 'overall' effectiveness increase with vaccination coverage in the population. Furthermore, we show how the measures of vaccine efficacy and vaccine effectiveness can be correctly calculated. CONCLUSIONS Typical parameterization of vaccine efficacy in mathematical models may underestimate the actual protective effect of the vaccine, resulting in discordance between the actual effects of vaccination at the population level and predictions made by models. This work shows how models can be correctly parameterized from clinical trial data.
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Bairwa M, Rajput M, Khanna P, Rohilla R, Verma R, Chawla S. Malaria vaccine: a bright prospect for elimination of malaria. Hum Vaccin Immunother 2012; 8:819-22. [PMID: 22739688 DOI: 10.4161/hv.20145] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Abstract
Malaria remains one of the few diseases those continue to scourge human civilization despite the significant advances in disease control strategies over the last century. Malaria is responsible for more than 500 million cases and 1-3 million deaths annually. Approximately 85% of these deaths are among children, mostly in Africa, primarily due to P. falciparum. Whole cell vaccines, irradiated sporozoites and genetically attenuated sporozoites have demonstrated long lasting, sterile protection against plasmodium infection in animal and experimental clinical studies. Atypical membrane protein 1 and merozoite surface protein 1 are the two most extensively studied asexual blood stage vaccine candidates. The most promising candidate vaccine under development is RTS, S combined with AS01 adjuvant. Initial results from phase III trials of this candidate vaccine show 50% reduction of malaria in 5-17 mo aged children during the 12 mo after vaccination. WHO anticipates that the RTS,S/AS01 vaccine will be recommended for the 6-14 week age group for co-administration together with other vaccines as part of routine immunization programs in malaria endemic countries. Malaria vaccine could play an important role in elimination and eventual eradication of malaria.
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Roestenberg M, de Vlas SJ, Nieman AE, Sauerwein RW, Hermsen CC. Efficacy of preerythrocytic and blood-stage malaria vaccines can be assessed in small sporozoite challenge trials in human volunteers. J Infect Dis 2012; 206:319-23. [PMID: 22615322 DOI: 10.1093/infdis/jis355] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
The development of a vaccine against malaria has public health priority. In a controlled setting, preliminary data on the efficacy of Plasmodium falciparum vaccine candidates can be obtained by exposing immunized human volunteers to the bites of laboratory-reared P. falciparum-infected mosquitoes. Using empirical data, we show that these trials, with small numbers of volunteers, are sufficiently powered to detect protective biological effects induced by preerythrocytic and/or blood-stage candidate vaccines if parasitemia is measured daily by quantitative polymerase chain reaction. Sporozoite challenge trials are thus a powerful tool for early selection of candidates that warrant efficacy of trials in the field.
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Affiliation(s)
- Meta Roestenberg
- Department of Medical Microbiology, Radboud University Nijmegen Medical Center, Nijmegen, the Netherlands.
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Estimating individual exposure to malaria using local prevalence of malaria infection in the field. PLoS One 2012; 7:e32929. [PMID: 22479349 PMCID: PMC3315550 DOI: 10.1371/journal.pone.0032929] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2011] [Accepted: 02/06/2012] [Indexed: 11/24/2022] Open
Abstract
Background Heterogeneity in malaria exposure complicates survival analyses of vaccine efficacy trials and confounds the association between immune correlates of protection and malaria infection in longitudinal studies. Analysis may be facilitated by taking into account the variability in individual exposure levels, but it is unclear how exposure can be estimated at an individual level. Method and Findings We studied three cohorts (Chonyi, Junju and Ngerenya) in Kilifi District, Kenya to assess measures of malaria exposure. Prospective data were available on malaria episodes, geospatial coordinates, proximity to infected and uninfected individuals and residence in predefined malaria hotspots for 2,425 individuals. Antibody levels to the malaria antigens AMA1 and MSP1142 were available for 291 children from Junju. We calculated distance-weighted local prevalence of malaria infection within 1 km radius as a marker of individual's malaria exposure. We used multivariable modified Poisson regression model to assess the discriminatory power of these markers for malaria infection (i.e. asymptomatic parasitaemia or clinical malaria). The area under the receiver operating characteristic (ROC) curve was used to assess the discriminatory power of the models. Local malaria prevalence within 1 km radius and AMA1 and MSP1142 antibodies levels were independently associated with malaria infection. Weighted local malaria prevalence had an area under ROC curve of 0.72 (95%CI: 0.66–0.73), 0.71 (95%CI: 0.69–0.73) and 0.82 (95%CI: 0.80–0.83) among cohorts in Chonyi, Junju and Ngerenya respectively. In a small subset of children from Junju, a model incorporating weighted local malaria prevalence with AMA1 and MSP1142 antibody levels provided an AUC of 0.83 (95%CI: 0.79–0.88). Conclusion We have proposed an approach to estimating the intensity of an individual's malaria exposure in the field. The weighted local malaria prevalence can be used as individual marker of malaria exposure in malaria vaccine trials and longitudinal studies of natural immunity to malaria.
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Smith T, Ross A, Maire N, Chitnis N, Studer A, Hardy D, Brooks A, Penny M, Tanner M. Ensemble modeling of the likely public health impact of a pre-erythrocytic malaria vaccine. PLoS Med 2012; 9:e1001157. [PMID: 22272189 PMCID: PMC3260300 DOI: 10.1371/journal.pmed.1001157] [Citation(s) in RCA: 91] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/31/2011] [Accepted: 11/30/2011] [Indexed: 11/18/2022] Open
Abstract
BACKGROUND The RTS,S malaria vaccine may soon be licensed. Models of impact of such vaccines have mainly considered deployment via the World Health Organization's Expanded Programme on Immunization (EPI) in areas of stable endemic transmission of Plasmodium falciparum, and have been calibrated for such settings. Their applicability to low transmission settings is unclear. Evaluations of the efficiency of different deployment strategies in diverse settings should consider uncertainties in model structure. METHODS AND FINDINGS An ensemble of 14 individual-based stochastic simulation models of P. falciparum dynamics, with differing assumptions about immune decay, transmission heterogeneity, and treatment access, was constructed. After fitting to an extensive library of field data, each model was used to predict the likely health benefits of RTS,S deployment, via EPI (with or without catch-up vaccinations), supplementary vaccination of school-age children, or mass vaccination every 5 y. Settings with seasonally varying transmission, with overall pre-intervention entomological inoculation rates (EIRs) of two, 11, and 20 infectious bites per person per annum, were considered. Predicted benefits of EPI vaccination programs over the simulated 14-y time horizon were dependent on duration of protection. Nevertheless, EPI strategies (with an initial catch-up phase) averted the most deaths per dose at the higher EIRs, although model uncertainty increased with EIR. At two infectious bites per person per annum, mass vaccination strategies substantially reduced transmission, leading to much greater health effects per dose, even at modest coverage. CONCLUSIONS In higher transmission settings, EPI strategies will be most efficient, but vaccination additional to the EPI in targeted low transmission settings, even at modest coverage, might be more efficient than national-level vaccination of infants. The feasibility and economics of mass vaccination, and the circumstances under which vaccination will avert epidemics, remain unclear. The approach of using an ensemble of models provides more secure conclusions than a single-model approach, and suggests greater confidence in predictions of health effects for lower transmission settings than for higher ones.
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Affiliation(s)
- Thomas Smith
- Swiss Tropical and Public Health Institute, Basel, Switzerland.
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Agnandji ST, Lell B, Soulanoudjingar SS, Fernandes JF, Abossolo BP, Conzelmann C, Methogo BGNO, Doucka Y, Flamen A, Mordmüller B, Issifou S, Kremsner PG, Sacarlal J, Aide P, Lanaspa M, Aponte JJ, Nhamuave A, Quelhas D, Bassat Q, Mandjate S, Macete E, Alonso P, Abdulla S, Salim N, Juma O, Shomari M, Shubis K, Machera F, Hamad AS, Minja R, Mtoro A, Sykes A, Ahmed S, Urassa AM, Ali AM, Mwangoka G, Tanner M, Tinto H, D'Alessandro U, Sorgho H, Valea I, Tahita MC, Kaboré W, Ouédraogo S, Sandrine Y, Guiguemdé RT, Ouédraogo JB, Hamel MJ, Kariuki S, Odero C, Oneko M, Otieno K, Awino N, Omoto J, Williamson J, Muturi-Kioi V, Laserson KF, Slutsker L, Otieno W, Otieno L, Nekoye O, Gondi S, Otieno A, Ogutu B, Wasuna R, Owira V, Jones D, Onyango AA, Njuguna P, Chilengi R, Akoo P, Kerubo C, Gitaka J, Maingi C, Lang T, Olotu A, Tsofa B, Bejon P, Peshu N, Marsh K, Owusu-Agyei S, Asante KP, Osei-Kwakye K, Boahen O, Ayamba S, Kayan K, Owusu-Ofori R, Dosoo D, Asante I, Adjei G, Adjei G, Chandramohan D, Greenwood B, Lusingu J, Gesase S, Malabeja A, Abdul O, Kilavo H, Mahende C, Liheluka E, Lemnge M, Theander T, Drakeley C, Ansong D, Agbenyega T, Adjei S, Boateng HO, Rettig T, Bawa J, Sylverken J, Sambian D, Agyekum A, Owusu L, Martinson F, Hoffman I, Mvalo T, Kamthunzi P, Nkomo R, Msika A, Jumbe A, Chome N, Nyakuipa D, Chintedza J, Ballou WR, Bruls M, Cohen J, Guerra Y, Jongert E, Lapierre D, Leach A, Lievens M, Ofori-Anyinam O, Vekemans J, Carter T, Leboulleux D, Loucq C, Radford A, Savarese B, Schellenberg D, Sillman M, Vansadia P. First results of phase 3 trial of RTS,S/AS01 malaria vaccine in African children. N Engl J Med 2011; 365:1863-75. [PMID: 22007715 DOI: 10.1056/nejmoa1102287] [Citation(s) in RCA: 613] [Impact Index Per Article: 47.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/11/2023]
Abstract
BACKGROUND An ongoing phase 3 study of the efficacy, safety, and immunogenicity of candidate malaria vaccine RTS,S/AS01 is being conducted in seven African countries. METHODS From March 2009 through January 2011, we enrolled 15,460 children in two age categories--6 to 12 weeks of age and 5 to 17 months of age--for vaccination with either RTS,S/AS01 or a non-malaria comparator vaccine. The primary end point of the analysis was vaccine efficacy against clinical malaria during the 12 months after vaccination in the first 6000 children 5 to 17 months of age at enrollment who received all three doses of vaccine according to protocol. After 250 children had an episode of severe malaria, we evaluated vaccine efficacy against severe malaria in both age categories. RESULTS In the 14 months after the first dose of vaccine, the incidence of first episodes of clinical malaria in the first 6000 children in the older age category was 0.32 episodes per person-year in the RTS,S/AS01 group and 0.55 episodes per person-year in the control group, for an efficacy of 50.4% (95% confidence interval [CI], 45.8 to 54.6) in the intention-to-treat population and 55.8% (97.5% CI, 50.6 to 60.4) in the per-protocol population. Vaccine efficacy against severe malaria was 45.1% (95% CI, 23.8 to 60.5) in the intention-to-treat population and 47.3% (95% CI, 22.4 to 64.2) in the per-protocol population. Vaccine efficacy against severe malaria in the combined age categories was 34.8% (95% CI, 16.2 to 49.2) in the per-protocol population during an average follow-up of 11 months. Serious adverse events occurred with a similar frequency in the two study groups. Among children in the older age category, the rate of generalized convulsive seizures after RTS,S/AS01 vaccination was 1.04 per 1000 doses (95% CI, 0.62 to 1.64). CONCLUSIONS The RTS,S/AS01 vaccine provided protection against both clinical and severe malaria in African children. (Funded by GlaxoSmithKline Biologicals and the PATH Malaria Vaccine Initiative; RTS,S ClinicalTrials.gov number, NCT00866619 .).
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Ross A, Smith T. Interpreting malaria age-prevalence and incidence curves: a simulation study of the effects of different types of heterogeneity. Malar J 2010; 9:132. [PMID: 20478060 PMCID: PMC2888834 DOI: 10.1186/1475-2875-9-132] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/04/2010] [Accepted: 05/17/2010] [Indexed: 11/18/2022] Open
Abstract
Background Individuals in a malaria endemic community differ from one another. Many of these differences, such as heterogeneities in transmission or treatment-seeking behaviour, affect malaria epidemiology. The different kinds of heterogeneity are likely to be correlated. Little is known about their impact on the shape of age-prevalence and incidence curves. In this study, the effects of heterogeneity in transmission, treatment-seeking and risk of co-morbidity were simulated. Methods Simple patterns of heterogeneity were incorporated into a comprehensive individual-based model of Plasmodium falciparum malaria epidemiology. The different types of heterogeneity were systematically simulated individually, and in independent and co-varying pairs. The effects on age-curves for parasite prevalence, uncomplicated and severe episodes, direct and indirect mortality and first-line treatments and hospital admissions were examined. Results Different heterogeneities affected different outcomes with large effects reserved for outcomes which are directly affected by the action of the heterogeneity rather than via feedback on acquired immunity or fever thresholds. Transmission heterogeneity affected the age-curves for all outcomes. The peak parasite prevalence was reduced and all age-incidence curves crossed those of the reference scenario with a lower incidence in younger children and higher in older age-groups. Heterogeneity in the probability of seeking treatment reduced the peak incidence of first-line treatment and hospital admissions. Heterogeneity in co-morbidity risk showed little overall effect, but high and low values cancelled out for outcomes directly affected by its action. Independently varying pairs of heterogeneities produced additive effects. More variable results were produced for co-varying heterogeneities, with striking differences compared to independent pairs for some outcomes which were affected by both heterogeneities individually. Conclusions Different kinds of heterogeneity both have different effects and affect different outcomes. Patterns of co-variation are also important. Alongside the absolute levels of different factors affecting age-curves, patterns of heterogeneity should be considered when parameterizing or validating models, interpreting data and inferring from one outcome to another.
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Affiliation(s)
- Amanda Ross
- Department of Epidemiology and Public Health, Swiss Tropical and Public Health Institute, Basel, Switzerland.
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