A recent study published by The Lancet examines the effectiveness of Euvichol-Plus, a killed whole-cell oral cholera vaccine (kOCV), in stimulating the immune system to combat the potentially fatal bacterial disease caused by Vibrio cholerae. A single administration of Euvichol-Plus demonstrated effectiveness in preventing medically attended cholera for a minimum of 36 months in the regions where cholera is endemic. While the data suggest short-term comparable protective effects in both young children and others, there is a notable decline in immunity among children under 5 years old during the third year following vaccination.
The investigators recruited 658 participants with confirmed cholera cases and 2274 matched individuals for the control group. Among the case group, 99 individuals (15.1%) were under 5 years old at the time of vaccination. The adjusted effectiveness of the single-dose vaccine was 52.7% (95% CI 31.4 to 67.4) at 12-17 months post-vaccination and 44.7% (24.8 to 59.4) at 24-36 months post-vaccination.
“Before this study, only 1 estimate of single-dose protection of a kOCV in children aged 1–4 years had been published. This trial, in Bangladesh, suggested that young children did not benefit from a single dose of Shanchol, even during the first 6 months after vaccination,” according to investigators. “By contrast, we found evidence that the population younger than 5 years in Uvira benefited from similar levels of protection to those aged 5 years and older at 12–17 months after vaccination; however, the point estimates dropped substantially in the third year after vaccination with CIs spanning the null.”1
While vaccine protection during the first 12-17 months after vaccination was comparable between children aged 1-4 years and older individuals, the effectiveness in 1-4-year-old children seemed to diminish in the third year following vaccination (adjusted vaccine effectiveness 32.9%, 95% CI -30.7 to 65.5), with confidence intervals including the possibility of no effect.
In this matched case-control research, investigators enrolled individuals with medically confirmed cholera who were treated at 2 cholera treatment centers in Uvira City, Democratic Republic of the Congo. In Uvira, 37.2% of households primarily used surface water for their drinking needs. In areas adjacent to rivers with limited tap water, over 80% of households used Escherichia coli-contaminated water. Additionally, these surveys found that 48.2% of the population depended solely on tap water for drinking.
3 Key Takeaways
- The study demonstrates that a single dose of this vaccine can provide considerable protection against cholera for at least 36 months in endemic regions.
- While the vaccine offers comparable protection for both young children (under 5 years) and older individuals in the initial 12-17 months post-vaccination, its effectiveness in children aged 1-4 years appears to decline in the third year after vaccination.
- There is an association between cholera and poverty-related factors such as inadequate access to clean water, poor sanitation, and lack of basic hygiene facilities.
The Centers for Disease Control and Prevention (CDC) explains, “Prevention of cholera is dependent on access to safe water, adequate sanitation, and basic hygiene needs. The following materials cover the basics of cholera and other diarrheal disease prevention.”2
“Our results confirm the associations between cholera and markers of poverty, such as using a shared latrine, using an unimproved source for drinking water, and not having electricity in the household,” according to investigators. “Although kOCV provides protection against cholera, tackling fundamental risk factors such as access to safe water and sanitation are needed to sustainably control the disease.”1
The study had limitations, as few vaccinated cases group members had vaccination cards, raising concerns about recall bias in a region with frequent vaccination campaigns. Efforts to minimize bias in vaccination status classification included visual aids and structured questions, but enumerator blinding was not implemented during control group enrollment. Variations in study protocols across periods posed interpretative challenges, yet sensitivity analyses supported consistent findings. Additionally, the retrospective nature of control group recruitment and the small sample size of children under 5 in the case group may have impacted the robustness of vaccine effectiveness estimates, particularly for two-dose protection due to low coverage and reporting uncertainties.
All in all, cholera is a significant global public health concern, especially in regions with limited access to clean water and adequate sanitation. While further research across various environments and over extended periods is necessary, the study contributes to the investigation regarding the effectiveness of a single kOCV dose, specifically focusing on Euvichol-Plus, which is the most extensively used cholera vaccine currently available.
References
- Bwenge Malembaka E, Bugeme P, Hutchins C, et. al. Effectiveness of one dose of killed oral cholera vaccine in an endemic community in the democratic republic of the congo: a matched case-control study. The Lancet. Published January 18, 2024. Accessed January 29, 2024. doi:https://doi.org/10.1016/S1473-3099(23)00742-9
- Cholera - vibrio cholerae infection. CDC. Published November 17, 2022. Accessed January 29, 2024. https://www.cdc.gov/cholera/prevention.html
