Franke MF, et al. - Researchers determined the duration of protection of the standard two-dose regimen of killed, bivalent, whole-cell oral cholera vaccination and an incomplete regimen of one dose up to 4 years after vaccination in Haiti. They found that single-dose vaccination offered short-term protection, and in order to ensure long-term protection, which lasted up to 4 years after vaccination, vaccination with two doses was needed. Based on these findings, killed, bivalent, whole-cell oral cholera vaccination should be a component of comprehensive cholera control plans.

Methods

• This case-control study was performed in the setting of two-dose vaccination campaigns with a killed, bivalent, whole-cell oral cholera vaccination, from October, 2012 through November, 2016.
• Participants included residents in the vaccine catchment area (Artibonite Department or Central Department) where they were recruited at the start of the study; and subjects eligible for the vaccination campaign (ie, aged ≥12 months, not pregnant, and living in the region at the time of the vaccine campaign).
• Cholera treatment centres were searched for patients with cholera and a positive stool culture.
• Matching of community controls to people with cholera by age group, time, and neighbourhood, was carried out.
• Researchers calculated vaccine effectiveness and examined heterogeneity in effectiveness over time via adjusted matched regression analyses.
• They assessed the efficacy of one and two oral cholera doses vs zero doses from 2 months to 48 months after vaccination, measured by self reporting.

Results

• A total of 178 people were assigned to the case group and 706 to the control group.
• Follow-up of these subjects did not reveal decrease in two-dose effectiveness.
• Adjusted analyses revealed 76% to be the estimated average cumulative 4 year effectiveness for two doses (95% CI 59–86).
• In contrast, findings revealed that single-dose effectiveness decreased over time in a log-linear fashion, with a predicted vaccine effectiveness of 79% at the end of 12 months (95% CI 43–93), which declined to zero before the end of the second year.