Reactive vaccination as an effective tool for measles outbreak control in measles mortality reduction settings, Democratic Republic of Congo, 2005-2006

Modelling control strategies for pneumococcal meningitis outbreaks in the African meningitis belt

INTRODUCTION

Pneumococcal meningitis outbreaks occur sporadically in the African meningitis belt. Outbreak control guidelines and interventions are well established for meningococcal but not pneumococcal meningitis. Mathematical modelling is a useful tool for assessing the potential impact of different pneumococcal control strategies. This work aimed to estimate the impact of reactive vaccination with pneumococcal conjugate vaccine (PCV) had it been implemented in past African meningitis belt outbreaks and assess their efficiency relative to existing routine infant immunisation with PCV.

METHODS & RESULTS

Using recent pneumococcal meningitis outbreaks in Burkina Faso, Chad, and Ghana as case studies, we investigated the potential impact of reactive vaccination. We calculated the number needed to vaccinate to avert one case (NNV) in each outbreak setting and over all outbreaks and compared this to the NNV for existing routine infant vaccination. We extended previous analyses of reactive vaccination by considering longer-term protection in vaccinees over five years, incorporating a proxy for indirect effects. We found that implementing reactive vaccination in previous pneumococcal meningitis outbreaks could have averted up to 10-20 % of outbreak cases, with the biggest potential impact in Brong Ahafo, Ghana (2015-2016) and Goundi, Chad (2009). The NNV, and hence the value of reactive vaccination, varied greatly. 'Large' (80 + cumulative modelled cases per 100,000 population) and/or 'prolonged' (exceeding a response threshold of 10 suspected cases per 100,000 per week for four weeks or more) outbreaks had NNV estimates under 10,000. For routine infant vaccination with PCV, the estimated NNV ranged from 3,100-5,600 in Burkina Faso and 1,500-2,600 in Ghana.

IMPLICATIONS

This analysis provides evidence to inform the design of pneumococcal meningitis outbreak response guidelines. Countries should consider reactive vaccination in each outbreak event, together with maintaining routine infant vaccination as the primary intervention to reduce pneumococcal disease burden and outbreak risk.

Cost-effectiveness analysis of typhoid conjugate vaccines in an outbreak setting: a modeling study

BACKGROUND

Several prolonged typhoid fever epidemics have been reported since 2010 throughout eastern and southern Africa, including Malawi, caused by multidrug-resistant Salmonella Typhi. The World Health Organization recommends the use of typhoid conjugate vaccines (TCVs) in outbreak settings; however, current data are limited on how and when TCVs might be introduced in response to outbreaks.

METHODOLOGY

We developed a stochastic model of typhoid transmission fitted to data from Queen Elizabeth Central Hospital in Blantyre, Malawi from January 1996 to February 2015. We used the model to evaluate the cost-effectiveness of vaccination strategies over a 10-year time horizon in three scenarios: (1) when an outbreak is likely to occur; (2) when an outbreak is unlikely to occur within the next ten years; and (3) when an outbreak has already occurred and is unlikely to occur again. We considered three vaccination strategies compared to the status quo of no vaccination: (a) preventative routine vaccination at 9 months of age; (b) preventative routine vaccination plus a catch-up campaign to 15 years of age; and (c) reactive vaccination with a catch-up campaign to age 15 (for Scenario 1). We also explored variations in outbreak definitions, delays in implementation of reactive vaccination, and the timing of preventive vaccination relative to the outbreak.

RESULTS

Assuming an outbreak occurs within 10 years, we estimated that the various vaccination strategies would prevent a median of 15-60% of disability-adjusted life-years (DALYs). Reactive vaccination was the preferred strategy for WTP values of $0-300 per DALY averted. For WTP values > $300, introduction of preventative routine TCV immunization with a catch-up campaign was the preferred strategy. Routine vaccination with a catch-up campaign was cost-effective for WTP values above $890 per DALY averted if no outbreak occurs and > $140 per DALY averted if implemented after the outbreak has already occurred.

CONCLUSIONS

Countries for which the spread of antimicrobial resistance is likely to lead to outbreaks of typhoid fever should consider TCV introduction. Reactive vaccination can be a cost-effective strategy, but only if delays in vaccine deployment are minimal; otherwise, introduction of preventive routine immunization with a catch-up campaign is the preferred strategy.

Public health responses during measles outbreaks in elimination settings: Strategies and challenges

In late September 2016, the Americas became the first region in the world to have eliminated endemic transmission of measles virus. Several other countries have also verified measles elimination, and countries in all six World Health Organization regions have adopted measles elimination goals. The public health strategies used to respond to measles outbreaks in elimination settings are thus becoming relevant to more countries. This review highlights the strategies used to limit measles spread in elimination settings: (1) assembly of an outbreak control committee; (2) isolation of measles cases while infectious; (3) exclusion and quarantining of individuals without evidence of immunity; (4) vaccination of susceptible individuals; (5) use of immunoglobulin to prevent measles in exposed susceptible high-risk persons; (6) and maintaining laboratory proficiency for confirmation of measles. Deciding on the extent of containment efforts should be based on the expected benefit of reactive interventions, balanced against the logistical challenges in implementing them.

Assessing the cost-effectiveness of different measles vaccination strategies for children in the Democratic Republic of Congo

INTRODUCTION

One of the goals of the Global Measles and Rubella Strategic Plan is the reduction in global measles mortality, with high measles vaccination coverage as one of its core components. While measles mortality has been reduced more than 79%, the disease remains a major cause of childhood vaccine preventable disease burden globally. Measles immunization requires a two-dose schedule and only countries with strong, stable immunization programs can rely on routine services to deliver the second dose. In the Democratic Republic of Congo (DRC), weak health infrastructure and lack of provision of the second dose of measles vaccine necessitates the use of supplementary immunization activities (SIAs) to administer the second dose.

METHODS

We modeled three vaccination strategies using an age-structured SIR (Susceptible-Infectious-Recovered) model to simulate natural measles dynamics along with the effect of immunization. We compared the cost-effectiveness of two different strategies for the second dose of Measles Containing Vaccine (MCV) to one dose of MCV through routine immunization services over a 15-year time period for a hypothetical birth cohort of 3 million children.

RESULTS

Compared to strategy 1 (MCV1 only), strategy 2 (MCV2 by SIA) would prevent a total of 5,808,750 measles cases, 156,836 measles-related deaths and save U.S. $199 million. Compared to strategy 1, strategy 3 (MCV2 by RI) would prevent a total of 13,232,250 measles cases, 166,475 measles-related deaths and save U.S. $408 million.

DISCUSSION

Vaccination recommendations should be tailored to each country, offering a framework where countries can adapt to local epidemiological and economical circumstances in the context of other health priorities. Our results reflect the synergistic effect of two doses of MCV and demonstrate that the most cost-effective approach to measles vaccination in DRC is to incorporate the second dose of MCV in the RI schedule provided that high enough coverage can be achieved.

Synthesis of Evidence to Characterize National Measles and Rubella Exposure and Immunization Histories

Population immunity depends on the dynamic levels of immunization coverage that countries achieve over time and any transmission of viruses that occur within the population that induce immunity. In the context of developing a dynamic transmission model for measles and rubella to support analyses of future immunization policy options, we assessed the model inputs required to reproduce past behavior and to provide some confidence about model performance at the national level. We reviewed the data available from the World Health Organization (WHO) and existing measles and rubella literature for evidence of historical reported routine and supplemental immunization activities and reported cases and outbreaks. We constructed model input profiles for 180 WHO member states and three other areas to support disease transmission model development and calibration. The profiles demonstrate the significant variability in immunization strategies used historically by regions and member states and the epidemiological implications of these historical choices. The profiles provide a historical perspective on measles and rubella immunization globally at the national level, and they may help immunization program managers identify existing immunity and/or knowledge gaps.

Modeling Measles Transmission in the North American Amish and Options for Outbreak Response

Measles outbreaks in the United States continue to occur in subpopulations with sufficient numbers of undervaccinated individuals, with a 2014 outbreak in Amish communities in Ohio pushing the annual cases to the highest national number reported in the last 20 years. We adapted an individual-based model developed to explore potential poliovirus transmission in the North American Amish to characterize a 1988 measles outbreak in the Pennsylvania Amish and the 2014 outbreak in the Ohio Amish. We explored the impact of the 2014 outbreak response compared to no or partial response. Measles can spread very rapidly in an underimmunized subpopulation like the North American Amish, with the potential for national spread within a year or so in the absence of outbreak response. Vaccination efforts significantly reduced the transmission of measles and the expected number of cases. Until global eradication, measles importations will continue to pose a threat to clusters of underimmunized individuals in the United States. Aggressive outbreak response efforts in Ohio probably prevented widespread transmission of measles within the entire North American Amish.

The effect of immunization on measles incidence in the Democratic Republic of Congo: Results from a model of surveillance data

BACKGROUND

Measles continues to be a leading cause of vaccine-preventable disease mortality among children under five despite a safe and efficacious vaccine being readily available. While global vaccination coverage has improved tremendously, measles outbreaks persist throughout sub-Saharan Africa. Since 2010, the Democratic Republic of Congo (DRC) has seen a resurgence of measles outbreaks affecting all 11 provinces. These outbreaks are mainly attributed to gaps in routine immunization (RI) coverage compounded with missed supplementary immunization activities (SIAs). We utilized national passive surveillance data from DRC's Integrated Disease Surveillance and Response (IDSR) system to estimate the effect of immunization on measles incidence in DRC.

METHODS

We investigated the decline in measles incidence post-immunization with one dose of measles containing vaccine (MCV1) with and without the addition of supplementary immunization activities (SIAs) and outbreak response immunization (ORI) campaigns. Measles case counts by health zone were obtained from the IDSR system between January 1, 2010 and December 31, 2013. The impact of measles immunization was modeled using a random effects multi-level model for count data with RI coverage levels and mass campaign activities from one year prior.

RESULTS

The presence of an SIA (aIRR [95% CI] 0.86 [0.60-1.25]) and ORI (0.28 [0.20-0.39]) in the year prior were both associated with a decrease in measles incidence. When interaction terms were included, our results suggested that the high levels of MCV1 reported in the year prior and the presence of either mass campaign was associated with a decrease in measles incidence.

CONCLUSIONS

Our results highlight the importance of a two-dose measles vaccine schedule and the need for a strong routine immunization program coupled with frequent SIAs. Repeated occurrences of large-scale outbreaks in DRC suggest that vaccination coverage rates are grossly overestimated and signify the importance of the evaluation and modification of measles prevention and control strategies.

Reactive vaccination in the presence of disease hotspots

Reactive vaccination has recently been adopted as an outbreak response tool for cholera and other infectious diseases. Owing to the global shortage of oral cholera vaccine, health officials must quickly decide who and where to distribute limited vaccine. Targeted vaccination in transmission hotspots (i.e. areas with high transmission efficiency) may be a potential approach to efficiently allocate vaccine, however its effectiveness will likely be context-dependent. We compared strategies for allocating vaccine across multiple areas with heterogeneous transmission efficiency. We constructed metapopulation models of a cholera-like disease and compared simulated epidemics where: vaccine is targeted at areas of high or low transmission efficiency, where vaccine is distributed across the population, and where no vaccine is used. We find that connectivity between populations, transmission efficiency, vaccination timing and the amount of vaccine available all shape the performance of different allocation strategies. In highly connected settings (e.g. cities) when vaccinating early in the epidemic, targeting limited vaccine at transmission hotspots is often optimal. Once vaccination is delayed, targeting the hotspot is rarely optimal, and strategies that either spread vaccine between areas or those targeted at non-hotspots will avert more cases. Although hotspots may be an intuitive outbreak control target, we show that, in many situations, the hotspot-epidemic proceeds so fast that hotspot-targeted reactive vaccination will prevent relatively few cases, and vaccination shared across areas where transmission can be sustained is often best.

Field evaluation of measles vaccine effectiveness among children in the Democratic Republic of Congo

BACKGROUND

Large-scale measles outbreaks in areas with high administrative vaccine coverage rates suggest the need to re-evaluate measles prevention and control in the Democratic Republic of Congo (DRC). Monitoring of measles Vaccine Effectiveness (VE) is a useful measure of quality control in immunization programs. We estimated measles VE among children aged 12-59 months in the Democratic Republic of Congo (DRC) using laboratory surveillance data from 2010-2012.

METHODS

We used the case-based surveillance system with laboratory confirmation to conduct a case-control study using the test negative design. Cases and controls were selected based on presence (n=1044) or absence (n=1335) of measles specific antibody IgM or epidemiologic linkage. Risk factors for measles were assessed using unconditional logistic regression, stratified by age.

RESULTS

Among children 12-59 months, measles vaccination was protective against measles [aOR (95%C)], 0.20 (0.15-0.26) and estimated VE was 80% (95% CI 74-85%). Year of diagnosis, 2011: 6.02 (4.16-8.72) and 2012; 8.31 (5.57-12.40) was a risk factor for measles when compared to 2010. Compared to Kinshasa, children in Bas-Congo, Kasai-Oriental, Maniema and South Kivu provinces all had higher odds of developing measles. Measles VE was similar for children 12-23 months and 24-59 months (80% and 81% respectively).

CONCLUSIONS

Repeated occurrences of measles outbreaks and lower than expected VE estimates suggest the need to further evaluate measles vaccine efficacy and improve vaccine delivery strategies in DRC.

Local discrepancies in measles vaccination opportunities: results of population-based surveys in Sub-Saharan Africa

BACKGROUND

The World Health Organization recommends African children receive two doses of measles containing vaccine (MCV) through routine programs or supplemental immunization activities (SIA). Moreover, children have an additional opportunity to receive MCV through outbreak response immunization (ORI) mass campaigns in certain contexts. Here, we present the results of MCV coverage by dose estimated through surveys conducted after outbreak response in diverse settings in Sub-Saharan Africa.

METHODS

We included 24 household-based surveys conducted in six countries after a non-selective mass vaccination campaign. In the majority (22/24), the survey sample was selected using probability proportional to size cluster-based sampling. Others used Lot Quality Assurance Sampling.

RESULTS

In total, data were collected on 60,895 children from 2005 to 2011. Routine coverage varied between countries (>95% in Malawi and Kirundo province (Burundi) while <35% in N'Djamena (Chad) in 2005), within a country and over time. SIA coverage was <75% in most settings. ORI coverage ranged from >95% in Malawi to 71.4% [95% CI: 68.9-73.8] in N'Djamena (Chad) in 2005.In five sites, >5% of children remained unvaccinated after several opportunities. Conversely, in Malawi and DRC, over half of the children eligible for the last SIA received a third dose of MCV.

CONCLUSIONS

Control pre-elimination targets were still not reached, contributing to the occurrence of repeated measles outbreak in the Sub-Saharan African countries reported here. Although children receiving a dose of MCV through outbreak response benefit from the intervention, ensuring that programs effectively target hard to reach children remains the cornerstone of measles control.

Measles in Democratic Republic of Congo: an outbreak description from Katanga, 2010-2011

Background

The Democratic Republic of Congo experiences regular measles outbreaks. From September 2010, the number of suspected measles cases increased, especially in Katanga province, where Medecins sans Frontieres supported the Ministry of Health in responding to the outbreak by providing free treatment, reinforcing surveillance and implementing non-selective mass vaccination campaigns. Here, we describe the measles outbreak in Katanga province in 2010–2011 and the results of vaccine coverage surveys conducted after the mass campaigns.

Methods

The surveillance system was strengthened in 28 of the 67 health zones of the province and we conducted seven vaccination coverage surveys in 2011.

Results

The overall cumulative attack rate was 0.71% and the case fatality ratio was 1.40%.

The attack rate was higher in children under 4 and decreased with age. This pattern was consistent across districts and time. The number of cases aged 10 years and older barely increased during the outbreak.

Conclusions

Early investigation of the age distribution of cases is a key to understanding the epidemic, and should guide the vaccination of priority age groups.

Effectiveness and timing of vaccination during school measles outbreak

Implementing a vaccination campaign during an outbreak can effectively reduce the outbreak size.

Body mass index and dental caries in children and adolescents: a systematic review of literature published 2004 to 2011

THE OBJECTIVE

The authors undertook an updated systematic review of the relationship between body mass index and dental caries in children and adolescents.

METHOD

The authors searched Medline, ISI, Cochrane, Scopus, Global Health and CINAHL databases and conducted lateral searches from reference lists for papers published from 2004 to 2011, inclusive. All empirical papers that tested associations between body mass index and dental caries in child and adolescent populations (aged 0 to 18 years) were included.

RESULTS

Dental caries is associated with both high and low body mass index.

CONCLUSION

A non-linear association between body mass index and dental caries may account for inconsistent findings in previous research. We recommend future research investigate the nature of the association between body mass index and dental caries in samples that include a full range of body mass index scores, and explore how factors such as socioeconomic status mediate the association between body mass index and dental caries.