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Saralamba S, Simpson JA, Choosri N, White L, Pan-Ngum W, Dondorp AM, White NJ. An artesunate pharmacometric model to explain therapeutic responses in falciparum malaria. J Antimicrob Chemother 2023; 78:2192-2202. [PMID: 37473441 PMCID: PMC10477127 DOI: 10.1093/jac/dkad219] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/29/2023] [Accepted: 06/29/2023] [Indexed: 07/22/2023] Open
Abstract
BACKGROUND The artemisinins are potent and widely used antimalarial drugs that are eliminated rapidly. A simple concentration-effect pharmacometric model does not explain why dosing more frequently than once daily fails to augment parasite clearance and improve therapeutic responses in vivo. Artemisinins can induce a temporary non-replicative or 'dormant' drug refractory state in Plasmodium falciparum malaria parasites which may explain recrudescences observed in clinical trials despite full drug susceptibility, but whether it explains the dosing-response relationship is uncertain. OBJECTIVES To propose a revised model of antimalarial pharmacodynamics that incorporates reversible asexual parasite injury and temporary drug refractoriness in order to explain the failure of frequent dosing to augment therapeutic efficacy in falciparum malaria. METHODS The model was fitted using a Bayesian Markov Chain Monte Carlo approach with the parasite clearance data from 39 patients with uncomplicated falciparum malaria treated with artesunate from western Cambodia and 40 patients from northwestern Thailand reported previously. RESULTS The revised model captured the dynamics of parasite clearance data. Its predictions are consistent with observed therapeutic responses. CONCLUSIONS A within-host pharmacometric model is proposed in which it is hypothesized that some malaria parasites enter a temporary drug refractory state after exposure to artemisinin antimalarials, which is followed by delayed parasite death or reactivation. The model fitted the observed sequential parasite density data from patients with acute P. falciparum malaria, and it supported reduced ring stage activity in artemisinin-resistant infections.
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Affiliation(s)
- Sompob Saralamba
- Mahidol Oxford Tropical Medicine Research Unit, Faculty of Tropical Medicine, Mahidol University, Bangkok, Thailand
| | - Julie A Simpson
- Centre for Epidemiology and Biostatistics, Melbourne School of Population and Global Health, The University of Melbourne, Melbourne, Victoria, Australia
| | - Noppon Choosri
- Center of Data Analytics and Knowledge Synthesis for Healthcare, Chiang Mai University, Chiang Mai, Thailand
| | - Lisa White
- Department of Biology, University of Oxford, Oxford, UK
| | - Wirichada Pan-Ngum
- Mahidol Oxford Tropical Medicine Research Unit, Faculty of Tropical Medicine, Mahidol University, Bangkok, Thailand
- Department of Tropical Hygiene, Faculty of Tropical Medicine, Mahidol University, Bangkok, Thailand
| | - Arjen M Dondorp
- Mahidol Oxford Tropical Medicine Research Unit, Faculty of Tropical Medicine, Mahidol University, Bangkok, Thailand
- Centre for Tropical Medicine and Global Health, Nuffield Department of Medicine, University of Oxford, Oxford, UK
| | - Nicholas J White
- Mahidol Oxford Tropical Medicine Research Unit, Faculty of Tropical Medicine, Mahidol University, Bangkok, Thailand
- Centre for Tropical Medicine and Global Health, Nuffield Department of Medicine, University of Oxford, Oxford, UK
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Chen J, Gao P, Xiao W, Cheng G, Krishna S, Wang J, Wong YK, Wang C, Gu L, Yang DH, Wang J. Multi-omics dissection of stage-specific artemisinin tolerance mechanisms in Kelch13-mutant Plasmodium falciparum. Drug Resist Updat 2023; 70:100978. [PMID: 37385107 DOI: 10.1016/j.drup.2023.100978] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/22/2023] [Revised: 05/31/2023] [Accepted: 06/01/2023] [Indexed: 07/01/2023]
Abstract
AIMS We investigated the stage-specific mechanisms of partial resistance to artemisinin (ART, an antimalarial drug) in Plasmodium falciparum (P. falciparum) carrying the Kelch13 C580Y mutation. METHODS Using fluorescence labeling and activity-based protein profiling, we systematically profile the ART activation levels in P. falciparum during the entire intra-erythrocytic developmental cycle (IDC), and determined the ART-targets profile of the ART-sensitive and -resistant strains at different stages. We retrieved and integrated datasets of single-cell transcriptomics and label-free proteomics across three IDC stages of wild-type P. falciparum. We also employed lipidomics to validate lipid metabolic reprogramming in the resistant strain. RESULTS The activation and expression patterns of genes and proteins of ART-targets in both ART-sensitive and resistant strains varied at different stages and periods of P. falciparum development, with the late trophozoite stage harboring the largest number of ART targets. We identified and validated 36 overlapping targets, such as GAPDH, EGF-1a, and SpdSyn, during the IDC stages in both strains. We revealed the ART-insensitivity of fatty acid-associated activities in the partially resistant strain at both the early ring and early trophozoite stages. CONCLUSIONS Our multi-omics strategies provide novel insights into the mechanisms of ART partial resistance in Kelch13 mutant P. falciparum, demonstrating the stage-specific interaction between ART and malaria parasites.
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Affiliation(s)
- Jiayun Chen
- Artemisinin Research Center, and Institute of Chinese Materia Medica, China Academy of Chinese Medical Sciences, Beijing 100700, China; Department of Critical Medicine, and Shenzhen Clinical Research Centre for Geriatrics, Shenzhen People's Hospital, First Affiliated Hospital of Southern University of Science and Technology, Shenzhen 518020, Guangdong, China
| | - Peng Gao
- Artemisinin Research Center, and Institute of Chinese Materia Medica, China Academy of Chinese Medical Sciences, Beijing 100700, China
| | - Wei Xiao
- Key Laboratory of Glucolipid Metabolic Disorder, Ministry of Education, Guangdong Pharmaceutical University, Guangzhou 510006, Guangdong, China
| | - Guangqing Cheng
- Artemisinin Research Center, and Institute of Chinese Materia Medica, China Academy of Chinese Medical Sciences, Beijing 100700, China
| | - Sanjeev Krishna
- Clinical Academic Group in Institute for Infection & Immunity, St George's University of London, London, United Kingdom; St George's University Hospitals NHS Foundation Trust, United Kingdom; Institut für Tropenmedizin, Universitätsklinikum Tübingen, Tübingen, Germany
| | - Jianyou Wang
- Artemisinin Research Center, and Institute of Chinese Materia Medica, China Academy of Chinese Medical Sciences, Beijing 100700, China
| | - Yin Kwan Wong
- Department of Critical Medicine, and Shenzhen Clinical Research Centre for Geriatrics, Shenzhen People's Hospital, First Affiliated Hospital of Southern University of Science and Technology, Shenzhen 518020, Guangdong, China
| | - Chen Wang
- Artemisinin Research Center, and Institute of Chinese Materia Medica, China Academy of Chinese Medical Sciences, Beijing 100700, China
| | - Liwei Gu
- Artemisinin Research Center, and Institute of Chinese Materia Medica, China Academy of Chinese Medical Sciences, Beijing 100700, China
| | - Dong Hua Yang
- New York College of Traditional Chinese Medicine Mineola, United States.
| | - Jigang Wang
- Artemisinin Research Center, and Institute of Chinese Materia Medica, China Academy of Chinese Medical Sciences, Beijing 100700, China; Department of Critical Medicine, and Shenzhen Clinical Research Centre for Geriatrics, Shenzhen People's Hospital, First Affiliated Hospital of Southern University of Science and Technology, Shenzhen 518020, Guangdong, China.
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Dimeric Artesunate Glycerophosphocholine Conjugate Nano-Assemblies as Slow-Release Antimalarials to Overcome Kelch 13 Mutant Artemisinin Resistance. Antimicrob Agents Chemother 2022; 66:e0206521. [PMID: 35416709 DOI: 10.1128/aac.02065-21] [Citation(s) in RCA: 10] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
Current best practice for the treatment of malaria relies on short half-life artemisinins that are failing against emerging Kelch 13 mutant parasite strains. Here, we introduce a liposome-like self-assembly of a dimeric artesunate glycerophosphocholine conjugate (dAPC-S) as an amphiphilic prodrug for the short-lived antimalarial drug, dihydroartemisinin (DHA), with enhanced killing of Kelch 13 mutant artemisinin-resistant parasites. Cryo-electron microscopy (cryoEM) images and the dynamic light scattering (DLS) technique show that dAPC-S typically exhibits a multilamellar liposomal structure with a size distribution similar to that of the liposomes generated using thin-film dispersion (dAPC-L). Liquid chromatography-mass spectrometry (LCMS) was used to monitor the release of DHA. Sustainable release of DHA from dAPC-S and dAPC-L assemblies increased the effective dose and thus efficacy against Kelch 13 mutant artemisinin-resistant parasites in an in vitro assay. To better understand the enhanced killing effect, we investigated processes for deactivation of both the assemblies and DHA, including the roles of serum components and trace levels of iron. Analysis of parasite proteostasis pathways revealed that dAPC assemblies exert their activity via the same mechanism as DHA. We conclude that this easily prepared multilamellar liposome-like dAPC-S with long-acting efficacy shows potential for the treatment of severe and artemisinin-resistant malaria.
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Zaloumis SG, Whyte JM, Tarning J, Krishna S, McCaw JM, Cao P, White MT, Dini S, Fowkes FJI, Maude RJ, Kremsner P, Dondorp A, Price RN, White NJ, Simpson JA. Development and Validation of an In Silico Decision Tool To Guide Optimization of Intravenous Artesunate Dosing Regimens for Severe Falciparum Malaria Patients. Antimicrob Agents Chemother 2021; 65:e02346-20. [PMID: 33685888 PMCID: PMC8316083 DOI: 10.1128/aac.02346-20] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/09/2020] [Accepted: 02/25/2021] [Indexed: 01/13/2023] Open
Abstract
Most deaths from severe falciparum malaria occur within 24 h of presentation to a hospital. Intravenous (i.v.) artesunate is the first-line treatment for severe falciparum malaria, but its efficacy may be compromised by delayed parasitological responses. In patients with severe malaria, the life-saving benefit of the artemisinin derivatives is their ability to clear circulating parasites rapidly, before they can sequester and obstruct the microcirculation. To evaluate the dosing of i.v. artesunate for the treatment of artemisinin-sensitive and reduced ring stage sensitivity to artemisinin severe falciparum malaria infections, Bayesian pharmacokinetic-pharmacodynamic modeling of data from 94 patients with severe malaria (80 children from Africa and 14 adults from Southeast Asia) was performed. Assuming that delayed parasite clearance reflects a loss of ring stage sensitivity to artemisinin derivatives, the median (95% credible interval) percentage of patients clearing ≥99% of parasites within 24 h (PC24≥99%) for standard (2.4 mg/kg body weight i.v. artesunate at 0 and 12 h) and simplified (4 mg/kg i.v. artesunate at 0 h) regimens was 65% (52.5% to 74.5%) versus 44% (25% to 61.5%) for adults, 62% (51.5% to 74.5%) versus 39% (20.5% to 58.5%) for larger children (≥20 kg), and 60% (48.5% to 70%) versus 36% (20% to 53.5%) for smaller children (<20 kg). The upper limit of the credible intervals for all regimens was below a PC24≥99% of 80%, a threshold achieved on average in clinical studies of severe falciparum malaria infections. In severe falciparum malaria caused by parasites with reduced ring stage susceptibility to artemisinin, parasite clearance is predicted to be slower with both the currently recommended and proposed simplified i.v. artesunate dosing regimens.
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Affiliation(s)
- Sophie G Zaloumis
- Centre for Epidemiology & Biostatistics, Melbourne School of Population and Global Health, University of Melbourne, Melbourne, Australia
| | - Jason M Whyte
- Centre of Excellence for Biosecurity Risk Analysis, School of BioSciences, University of Melbourne, Melbourne, Australia
- Australian Research Council Centre of Excellence for Mathematical and Statistical Frontiers, School of Mathematics and Statistics, University of Melbourne, Melbourne, Australia
| | - Joel Tarning
- Mahidol-Oxford Tropical Medicine Research Unit, Faculty of Tropical Medicine, Mahidol University, Bangkok, Thailand
- Centre for Tropical Medicine and Global Health, Nuffield Department of Medicine, University of Oxford, Oxford, United Kingdom
| | - Sanjeev Krishna
- Institute for Infection and Immunity, St. George's Hospital, University of London, London, United Kingdom
| | - James M McCaw
- Centre for Epidemiology & Biostatistics, Melbourne School of Population and Global Health, University of Melbourne, Melbourne, Australia
- School of Mathematics and Statistics, University of Melbourne, Melbourne, Australia
| | - Pengxing Cao
- School of Mathematics and Statistics, University of Melbourne, Melbourne, Australia
| | - Michael T White
- Department of Parasites and Insect Vectors, Institut Pasteur, Paris, France
| | - Saber Dini
- Centre for Epidemiology & Biostatistics, Melbourne School of Population and Global Health, University of Melbourne, Melbourne, Australia
| | - Freya J I Fowkes
- Centre for Epidemiology & Biostatistics, Melbourne School of Population and Global Health, University of Melbourne, Melbourne, Australia
- Disease Elimination Program, Burnet Institute, Melbourne, Australia
| | - Richard J Maude
- Mahidol-Oxford Tropical Medicine Research Unit, Faculty of Tropical Medicine, Mahidol University, Bangkok, Thailand
- Centre for Tropical Medicine and Global Health, Nuffield Department of Medicine, University of Oxford, Oxford, United Kingdom
- Harvard TH Chan School of P`ublic Health, Harvard University, Boston, Massachusetts, USA
| | - Peter Kremsner
- Centre de Recherches Médicales de Lambaréné, Lambaréné, Gabon
- Gabon and Institut für Tropenmedizin, University of Tübingen, Tübingen, Germany
| | - Arjen Dondorp
- Mahidol-Oxford Tropical Medicine Research Unit, Faculty of Tropical Medicine, Mahidol University, Bangkok, Thailand
- Centre for Tropical Medicine and Global Health, Nuffield Department of Medicine, University of Oxford, Oxford, United Kingdom
| | - Ric N Price
- Centre for Tropical Medicine and Global Health, Nuffield Department of Medicine, University of Oxford, Oxford, United Kingdom
- Global Health Division, Menzies School of Health Research and Charles Darwin University, Darwin, Northern Territory, Australia
| | - Nicholas J White
- Mahidol-Oxford Tropical Medicine Research Unit, Faculty of Tropical Medicine, Mahidol University, Bangkok, Thailand
- Centre for Tropical Medicine and Global Health, Nuffield Department of Medicine, University of Oxford, Oxford, United Kingdom
| | - Julie A Simpson
- Centre for Epidemiology & Biostatistics, Melbourne School of Population and Global Health, University of Melbourne, Melbourne, Australia
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Khoury DS, Aogo R, Randriafanomezantsoa-Radohery G, McCaw JM, Simpson JA, McCarthy JS, Haque A, Cromer D, Davenport MP. Within-host modeling of blood-stage malaria. Immunol Rev 2019; 285:168-193. [PMID: 30129195 DOI: 10.1111/imr.12697] [Citation(s) in RCA: 20] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
Malaria infection continues to be a major health problem worldwide and drug resistance in the major human parasite species, Plasmodium falciparum, is increasing in South East Asia. Control measures including novel drugs and vaccines are in development, and contributions to the rational design and optimal usage of these interventions are urgently needed. Infection involves the complex interaction of parasite dynamics, host immunity, and drug effects. The long life cycle (48 hours in the common human species) and synchronized replication cycle of the parasite population present significant challenges to modeling the dynamics of Plasmodium infection. Coupled with these, variation in immune recognition and drug action at different life cycle stages leads to further complexity. We review the development and progress of "within-host" models of Plasmodium infection, and how these have been applied to understanding and interpreting human infection and animal models of infection.
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Affiliation(s)
| | - Rosemary Aogo
- Kirby Institute, UNSW Sydney, Sydney, NSW, Australia
| | | | - James M McCaw
- School of Mathematics and Statistics, University of Melbourne, Melbourne, VIC, Australia.,Centre for Epidemiology and Biostatistics, Melbourne School of Population and Global Health, University of Melbourne, Melbourne, VIC, Australia.,Peter Doherty Institute for Infection and Immunity, The Royal Melbourne Hospital and University of Melbourne, Melbourne, VIC, Australia
| | - Julie A Simpson
- Centre for Epidemiology and Biostatistics, Melbourne School of Population and Global Health, University of Melbourne, Melbourne, VIC, Australia
| | - James S McCarthy
- QIMR Berghofer Medical Research Institute, Herston, QLD, Australia
| | - Ashraful Haque
- QIMR Berghofer Medical Research Institute, Herston, QLD, Australia
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Ozonide Antimalarial Activity in the Context of Artemisinin-Resistant Malaria. Trends Parasitol 2019; 35:529-543. [PMID: 31176584 DOI: 10.1016/j.pt.2019.05.002] [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] [Received: 10/31/2018] [Revised: 04/02/2019] [Accepted: 05/01/2019] [Indexed: 12/18/2022]
Abstract
The ozonides are one of the most advanced drug classes in the antimalarial development pipeline and were designed to improve on limitations associated with current front-line artemisinin-based therapies. Like the artemisinins, the pharmacophoric peroxide bond of ozonides is essential for activity, and it appears that these antimalarials share a similar mode of action, raising the possibility of cross-resistance. Resistance to artemisinins is associated with Plasmodium falciparum mutations that allow resistant parasites to escape short-term artemisinin-mediated damage (elimination half-life ~1 h). Importantly, some ozonides (e.g., OZ439) have a sustained in vivo drug exposure profile, providing a major pharmacokinetic advantage over the artemisinin derivatives. Here, we describe recent progress made towards understanding ozonide antimalarial activity and discuss ozonide utility within the context of artemisinin resistance.
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In Silico Investigation of the Decline in Clinical Efficacy of Artemisinin Combination Therapies Due to Increasing Artemisinin and Partner Drug Resistance. Antimicrob Agents Chemother 2018; 62:AAC.01292-18. [PMID: 30249691 DOI: 10.1128/aac.01292-18] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/17/2018] [Accepted: 09/13/2018] [Indexed: 01/08/2023] Open
Abstract
Antimalarial treatment currently relies on an artemisinin derivative and a longer-acting partner drug. With the emergence of resistance to the artemisinin derivatives and the potential pressure this exerts on the partner drugs, the impact of resistance to each drug on efficacy needs to be investigated. An in silico exploration of dihydroartemisinin-piperaquine and mefloquine-artesunate, two artemisinin-based combination therapies that are commonly used in Southeast Asia, was performed. The percentage of treatment failures was simulated from a within-host pharmacokinetic-pharmacodynamic (PKPD) model, assuming that parasites developed increasing levels of (i) artemisinin derivative resistance or (ii) concomitant resistance to both the artemisinin derivative and the partner drug. Because the exact nature of how resistant Plasmodium falciparum parasites respond to treatment is unknown, we examined the impact on treatment failure rates of artemisinin resistance that (i) reduced the maximal killing rate, (ii) increased the concentration of drug required for 50% killing, or (iii) shortened the window of parasite stages that were susceptible to artemisinin derivatives until the drugs had no effect on the ring stages. The loss of the ring-stage activity of the artemisinin derivative caused the greatest increase in the treatment failure rate, and this result held irrespective of whether partner drug resistance was assumed to be present or not. To capture the uncertainty regarding how artemisinin derivative and partner drug resistance affects the assumed concentration-killing effect relationship, a variety of changes to this relationship should be considered when using within-host PKPD models to simulate clinical outcomes to guide treatment strategies for resistant infections.
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Dini S, Zaloumis S, Cao P, Price RN, Fowkes FJI, van der Pluijm RW, McCaw JM, Simpson JA. Investigating the Efficacy of Triple Artemisinin-Based Combination Therapies for Treating Plasmodium falciparum Malaria Patients Using Mathematical Modeling. Antimicrob Agents Chemother 2018; 62:e01068-18. [PMID: 30150462 PMCID: PMC6201091 DOI: 10.1128/aac.01068-18] [Citation(s) in RCA: 39] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/24/2018] [Accepted: 08/07/2018] [Indexed: 01/13/2023] Open
Abstract
The first line treatment for uncomplicated falciparum malaria is artemisinin-based combination therapy (ACT), which consists of an artemisinin derivative coadministered with a longer-acting partner drug. However, the spread of Plasmodium falciparum resistant to both artemisinin and its partner drugs poses a major global threat to malaria control activities. Novel strategies are needed to retard and reverse the spread of these resistant parasites. One such strategy is triple artemisinin-based combination therapy (TACT). We developed a mechanistic within-host mathematical model to investigate the efficacy of a TACT (dihydroartemisinin-piperaquine-mefloquine [DHA-PPQ-MQ]) for use in South-East Asia, where DHA and PPQ resistance are now increasingly prevalent. Comprehensive model simulations were used to explore the degree to which the underlying resistance influences the parasitological outcomes. The effect of MQ dosing on the efficacy of TACT was quantified at various degrees of DHA and PPQ resistance. To incorporate interactions between drugs, a novel model is presented for the combined effect of DHA-PPQ-MQ, which illustrates how the interactions can influence treatment efficacy. When combined with a standard regimen of DHA and PPQ, the administration of three 6.7-mg/kg doses of MQ was sufficient to achieve parasitological efficacy greater than that currently recommended by World Health Organization (WHO) guidelines. As a result, three 8.3-mg/kg doses of MQ, the current WHO-recommended dosing regimen for MQ, combined with DHA-PPQ, has the potential to produce high cure rates in regions where resistance to DHA-PPQ has emerged.
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Affiliation(s)
- Saber Dini
- Centre for Epidemiology and Biostatistics, Melbourne School of Population and Global Health, University of Melbourne, Melbourne, Australia
| | - Sophie Zaloumis
- Centre for Epidemiology and Biostatistics, Melbourne School of Population and Global Health, University of Melbourne, Melbourne, Australia
| | - Pengxing Cao
- School of Mathematics and Statistics, University of Melbourne, Melbourne, Australia
| | - Ric N Price
- Global and Tropical Health Division, Menzies School of Health Research and Charles Darwin University, Casuarina, Australia
- Centre for Tropical Medicine and Global Health, Nuffield Department of Clinical Medicine, University of Oxford, Oxford, United Kingdom
| | - Freya J I Fowkes
- Centre for Epidemiology and Biostatistics, Melbourne School of Population and Global Health, University of Melbourne, Melbourne, Australia
- Burnet Institute, Disease Elimination Program, Public Health, Melbourne, Australia
- Department of Epidemiology and Preventative Medicine and Department of Infectious Diseases, Monash University, Melbourne, Australia
| | - Rob W van der Pluijm
- Centre for Tropical Medicine and Global Health, Nuffield Department of Clinical Medicine, University of Oxford, Oxford, United Kingdom
- Mahidol Oxford Tropical Medicine Research Unit, Bangkok, Thailand
| | - James M McCaw
- Centre for Epidemiology and Biostatistics, Melbourne School of Population and Global Health, University of Melbourne, Melbourne, Australia
- School of Mathematics and Statistics, University of Melbourne, Melbourne, Australia
- Peter Doherty Institute for Infection and Immunity, The Royal Melbourne Hospital and University of Melbourne, Melbourne, Australia
- Murdoch Children's Research Institute, The Royal Children's Hospital, Melbourne, Australia
| | - Julie A Simpson
- Centre for Epidemiology and Biostatistics, Melbourne School of Population and Global Health, University of Melbourne, Melbourne, Australia
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