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Abstract
Cholera is the most common dehydrating diarrhoeal disease in low and middle income countries (LMICs). In Bangladesh the disease is endemic, causing a substantial burden of morbidity and mortality. Oral cholera vaccines (OCVs) have been developed and improved over the last three decades as a protective tool to control cholera. The World Health Organization recommends the use of OCVs in humanitarian emergencies as well as in epidemic and endemic settings. However, OCV effectiveness has been shown to vary by setting, which suggests that the identification of the drivers of effectiveness is important when planning for strategic use of the vaccine in each setting.
This thesis aims to extend our insight on cholera vaccination and the drivers of vaccine effectiveness, which could be useful in improving vaccination strategies in LMICs where cholera is often endemic.
The thesis is a series of published peer-reviewed articles that include (i) improved approaches to vaccine delivery (ii) effectiveness of OCV stored at elevated temperatures (iii) risk factors for cholera in different disease transmission settings; and (iv) predictors of OCV uptake in a mass vaccination campaign.
In the first paper, there is discussion about cholera disease, different approaches of OCV implementation in endemic and epidemic situations, the role of herd immunity and factors affecting immunogenicity and the effectiveness of vaccine. The second paper demonstrates the safety, immunogenicity and thermostability of OCVs; keeping the vaccine at a higher temperature (up to 42°C) than the recommended stringent cold chain (2-8°C). The third paper assesses socioeconomic factors of risk for cholera in vaccinated and non-vaccinated communities to understand whether the risk differs by the disease transmission pattern. The fourth paper describes the experience of using a geographic information system (GIS) in the planning and delivery of OCVs in a clinical trial and identifies socioeconomic predictors which influence vaccine uptake in a low socioeconomic community in Bangladesh.
These studies provide evidence which will assist strategic implementation of cholera vaccination program in endemic settings. The findings of this thesis will inform policy makers to plan intervention strategies using OCV to reduce the burden of cholera with affordable vaccines globally.