The impact of mass cholera vaccination in Uvira, Democratic Republic of the Congo

While there is ample evidence on the direct protection conferred by killed whole-cell oral cholera vaccines (OCV), there is limited evidence documenting the population-level impacts of mass vaccination on infection rates, disease incidence and mortality both due to the limited number of mass campaigns that have been conducted in cholera-endemic areas and due to the generally weak clinical surveillance systems for cholera. As more and more vaccines become available and endemic hotspots plan to use OCV, evidence on the population level impacts of mass vaccination are needed to help set expectations for the role OCV can play in short- to medium-term global reductions in cholera. Eastern Democratic Republic of Congo provides a unique setting to study the impacts of mass vaccination given the reporting of cholera cases throughout the year and the ambitious plans by the Ministry of Health to substantially reduce cholera burden in the years to come through improvements in water and sanitation and the use of OCV.

Relevance

Results from this study will allow for a better estimation of the impact of mass oral cholera vaccination campaigns deployed in Uvira (South Kivu) on the incidence of confirmed clinical cholera and mortality. To further understand both direct and indirect effects of vaccination while more explicitly accounting for changes in population movement, secular changes and waning vaccine protection, we will fit dynamic transmission models to data from Uvira. A better understanding of these effects will also aid in the country’s national plan for cholera elimination over 2018-2022.

Objectives

There are three main objectives of this study. The first is to estimate the impact of mass oral cholera vaccination campaigns deployed in the city of Uvira on the incidence of confirmed clinical cholera and cholera-related mortality from 2021 through 2026. The second is to describe V. cholerae contamination patterns and genetic diversity over time in patients, households, and the broader environment through microbiological analyses of clinical and environmental samples. The third and final objective is to describe changes in vaccine coverage, care seeking behavior, and serologically-derived V. cholerae infections rates in the city of Uvira from 2021 to 2026.

Methods and Outcome measures / Variables

This study has three main components; surveillance for medically attended cholera, follow-up studies in households of confirmed cholera cases with environmental surveillance and representative household surveys.

For clinical surveillance, systematic cholera confirmation through RDT, culture and qPCR will be continuously conducted over the study period at the primary sites in Uvira for diarrhea/cholera treatment; a cholera treatment centre (CTC) and cholera treatment unit (CTU).

For household follow-up studies, environmental sampling in households of confirmed cholera cases as well as matched controls, and at community water sources will be conducted by study staff in addition to laboratory testing for V. cholerae via culture-based and molecular methods.

Representative household surveys will be conducted each year, with blood collection done in a subset (3 of the years). Data on migration patterns, vaccine coverage, access to and use of WASH infrastructure, household mortality and other data will be collected from all participating individuals within households. We will test serum for a suite of antibodies related to previous V. cholerae O1 infection and use machine learning models to estimate seroincidence. ”

We aim to quantify the impact of the killed oral cholera vaccine (OCV) on cholera incidence and mortality over 6 years (2021-2026) in Uvira, Democratic Republic of Congo, a city with endemic cholera transmission. In addition, we hope to better understand how contamination patterns and genetic diversity of the cholera-causing bacteria change over time (pre- and post-vaccination) through analysis of clinical and environmental samples.

This study will help us better understand the impact of mass cholera vaccination programs to set expectations for decision makers and help understand when revaccination may be needed.