5-Year effectiveness of an oral cholera vaccine in a cholera outbreak in rural Haiti: a case–control study

<h2>Summary</h2><h3>Background</h3> The World Health Organization recommends use of killed oral cholera vaccines (kOCV) as part of cholera prevention and control, but data on the duration of effectiveness of the most widely available vaccine, Euvichol® is limited. We evaluated the effectiveness of Euvichol® 5 years after a kOCV campaign conducted in Haiti in 2017. <h3>Methods</h3> We undertook a frequency-matched case–control study in Mirebalais, Haiti between October 2022 and February 2023. Cases were patients with acute watery diarrhea, had a stool sample positive for <i>V. cholerae</i> by polymerase chain reaction, and had been eligible for kOCV during the 2017 campaign. Cases were frequency-matched with community controls by age group and neighborhood. Participants reported sociodemographics, risk factors, and vaccination status. We used adjusted logistic regression analyses to estimate vaccine effectiveness (VE) of at least one kOCV dose versus none. <h3>Findings</h3> We analyzed 93 cases and 135 controls. 22% of the cases and 51% of the controls self-reported vaccination. Receiving Euvichol in 2017 was associated with a 5-year adjusted VE of 78% (95% CI: 57%–89%, p < 0.0001). <h3>Interpretation</h3> Receiving any Euvichol® effectively protected against cholera in Haiti, 5 years after a two-dose vaccination campaign. This has important implications for public health planning, especially in considering of the appropriate timing of boosting schedules and comparative effectiveness analyses. <h3>Funding</h3> US National Institute of Allergy and Infectious Diseases of the National Institutes of Health and the Gates Foundation.