# Effectiveness of a reactive oral cholera vaccination during a cholera outbreak at the Douala New-Bell Central Prison in Cameroon

## TL;DR

A study in a Cameroonian prison found that reactive oral cholera vaccination reduced hospitalizations during an outbreak, highlighting its value in high-risk, overcrowded settings.

## Contribution

This is one of the first studies to evaluate oral cholera vaccine effectiveness in a prison population during an outbreak.

## Key findings

- Vaccinated inmates had significantly lower odds of cholera-related hospitalization compared to unvaccinated inmates.
- Two doses of OCV provided stronger protection than one dose, with adjusted odds ratios of 0.37 for two doses.
- Improved living conditions in certain prison sections were associated with reduced cholera severity.

## Abstract

Research on cholera vaccine effectiveness in prison populations is scarce, despite evidence of OCV benefits in general outbreak settings. During a major cholera outbreak in Douala’s overcrowded central prison, Cameroon deployed the Euvichol oral cholera vaccine. This study assessed the vaccine’s association with reduced cholera-related hospitalisation among inmates.

A retrospective secondary data analysis was conducted in 2024 on inmates who were targeted for reactive vaccination during a cholera outbreak in 2022. A stratified sampling strategy based on gender and housing type was used to select eligible inmates. Vaccine status was ascertained from the prison’s vaccination register. Our outcome variable of interest was cholera-related hospitalisation. Logistic regression was used to assess the likelihood of hospitalisation for severe cholera among vaccinated and unvaccinated inmates. Adjusted odds ratios (aOR) and associated 95% confidence intervals (CI) were obtained.

A total of 323 inmates were included for analysis, of whom 110 (34.9%) were vaccinated. Cholera-related hospitalisations occurred in 147/213(57.3%) unvaccinated inmates compared to 45/110(41.7%) vaccinated inmates. For inmates who received one dose of OCV, hospitalisation was associated with an adjusted odds ratio of 0.39 (95% CI: 0.21–0.70; p = 0.002), while those who received two doses showed an adjusted OR of 0.37 (95% CI: 0.19–0.72; p = 0.003). In subgroup analyses, severe cholera was found to be associated with lower odds among female prisoners [aOR = 0.24, 95% CI: 0.08–0.70, p = 0.009] and among inmates in ‘VIP’ cells [aOR = 0.31, 95% CI: 0.11–0.84, p = 0.022].

Vaccination was associated with a reduction in hospitalisation during the prison cholera outbreak, confirming its emergency value. However, OCV alone may not be sufficient if overcrowding and poor water, sanitation, and hygiene (WASH) conditions persist. Improved living standards, as seen in the female and VIP sections, must be extended to all inmates.

This study evaluates the effectiveness of a reactive oral cholera vaccine (OCV) in controlling an outbreak at the Douala Central Prison in Cameroon. Cholera, a severe diarrheal disease caused by the bacterium Vibrio cholerae, is a major public health concern, particularly in overcrowded and unsanitary environments like prisons. The prison in Douala is a high-risk setting, with severe overcrowding and inadequate sanitation, making it vulnerable to cholera outbreaks.

The study found that inmates who received the OCV had significantly lower chances of being hospitalised due to cholera compared to those who did not receive the vaccine. The results show that even partial vaccination provides meaningful protection, and full vaccination offers the best results. The findings are important because they highlight how vaccines can be a crucial tool in preventing disease outbreaks in prisons, a setting often overlooked in public health strategies. These results not only support the use of vaccines in emergency responses but also emphasise the need for improved sanitation and healthcare access in overcrowded environments. This research contributes to a better understanding of how to manage cholera in high-risk, resource-limited settings.