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

Abstract

BackgroundA global shortage of cholera vaccines has increased use of single-dose regimens, rather than the standard two-dose regimen. There is limited evidence on single-dose protection, particularly in children. In late 2020 a mass vaccination campaign was conducted in Uvira, a cholera endemic urban setting in eastern Democratic Republic of the Congo. Coverage surveys showed that the majority of vaccinated people received only one dose. We examined the effectiveness of a single-dose of the oral cholera vaccine Euvichol-plus in this high-burden setting.MethodsIn this case-control study, we recruited medically-attended confirmed cholera cases and age-, sex-, and neighborhood-matched community controls during two distinct periods after mass vaccination, October 2021 to March 2022 (12-17 months post-vaccination) and October 2022 to May 2023 (24-31 months post-vaccination). The odds of vaccination in cases and controls were contrasted in conditional logistic regression models to estimate unadjusted and adjusted vaccine effectiveness.FindingsWe enrolled 432 confirmed cases and 1554 matched controls during the two study periods with 21.5% of cases being under five years old. The adjusted single-dose VE was 52% (95% CI: 32·3–66) 12-17 months post-vaccination and 40·8% (95% CI: 8·6–61·7) 24-31 months post-vaccination. Combining the two study periods led to an adjusted single-dose VE of 45% (95% CI 28·2–57·8), with no significant differences among children under five years old and older individuals.InterpretationA single-dose of Euvichol-Plus provided substantial protection against medically-attended cholera for at least 31 months post-vaccination in this cholera endemic setting.FundingThis work was supported by the Wellcome Trust and Gavi (GAVI-RFP-2019-062).