Evaluation of oral cholera vaccine (Euvichol-Plus) effectiveness against Vibrio cholerae in Bangladesh: an interim analysis.

Abstract

Introduction: Millions of Euvichol-Plus doses have been deployed from the global oral cholera vaccine stockpile in over 20 cholera-affected countries. However, information on Euvichol-Plus's effectiveness is limited. Using this vaccine in a cholera epidemic in Dhaka, Bangladesh, provided the opportunity to evaluate the vaccine effectiveness (VE) using a test-negative design.

Methods: A two-dose regimen of Euvichol-Plus was administered to individuals aged >1 year in a population of ca. 900 000 in two campaign rounds between June and August 2022, with prospective registration of all persons who received at least one dose. We conducted systematic surveillance in two key facilities, enrolling patients with acute watery diarrhoea who were eligible for vaccination from the campaign's start and who presented for care between 21 August 2022 and 20 August 2023. Faecal culture-positive cholera cases were matched to up to four faecal culture-negative controls by age, presentation date and facility. Vaccination status was documented without knowledge of culture results. Conditional logistic regression models estimated the OR for the vaccination-cholera association, and the VE of the two-dose regimen was calculated as [(1-OR) × 100].

Results: The analysis included 226 cases and 552 matched controls. The adjusted VE of two doses of the Euvichol-Plus vaccine against medically attended cholera was 66% (99.5% CI: 30 to 83) for all recipients. Limited protection (12%; 95% CI: -95 to 60) was observed for children aged 1-4 years; whereas, protection was 79% (95% CI: 60 to 89) for those aged ≥5 years. VE against cholera with moderate to severe dehydration was 69% (95% CI: 44 to 83) overall but 6% (95% CI: -206 to 71) for children aged 1-4 years.

Conclusion: Euvichol-Plus provided significant protection against medically attended cholera of any severity as well as cholera with moderate to severe dehydration. However, significant levels of protection were only observed for those aged ≥5 years.