Single-dose inactivated cholera vaccine regimen shows efficacy in Bangladesh

1. Previous studies have proven the efficacy of a killed whole-cell-only oral cholera vaccine administered as a two-dose regimen, which has been linked with 65% cumulative protection over 5 years of follow-up. 

2. In this randomized, placebo controlled trial, a single-dose regimen of inactivated cholera vaccine was linked with 40% vaccine efficacy against all cholera episodes and 63% vaccine efficacy against severely dehydrating cholera episodes among nonpregnant residents of Dhaka, Bangladesh over 6 months.

Evidence Rating Level: 1 (Excellent)

Study Rundown: Diarrheal illness caused by cholera is a major cause of mortality and morbidity globally. Previous studies have proven the efficacy of a killed whole-cell-only oral cholera vaccine administered as a two-dose regimen; data also pointed to substantial immunologic responses in recipients after the first dose.  This placebo-controlled, randomized trial, conducted among nonpregnant residents of a cholera-endemic region of Bangladesh, investigated whether there would be population-level efficacy and prevention of cholera-related illness by pursuing a single-dose vaccination schedule.

The study reports a 40% vaccine protective efficacy against all cholera episodes, with improved rates of 63% against severely dehydrating cholera episodes. These efficacy rates were collected over a six-month follow-up period. The findings were significant only for individuals vaccinated above or equal to the age of 5. The adverse event profiles were similar between intervention and placebo arms of the study.

These data suggest that there may be a role for single-dose oral cholera vaccine programs in cholera-endemic settings, such as Bangladesh, and also point to a silver lining for individuals enrolled in a two-dose regimen who may only receive one dose for a number of potential reasons. However, the results must be interpreted with caution as they only pertain to 6 months of follow-up time and emerge from one particular geographic region where cholera is highly epidemic.

Click to read the study, published today in NEJM

Relevant Reading: 5 year efficacy of a bivalent killed whole-cell oral cholera vaccine in Kolkata India: a cluster-randomized, double-blind, placebo-controlled trial

In-Depth [randomized controlled trial]: This randomized, placebo-controlled study initially screened 352,157 nonpregnant individuals in Dhaka, Bangladesh, an urban area in which cholera is highly epidemic. Of these, 102,552 received a single dose of the whole-cell-only oral cholera vaccine, and 102,148 received a placebo of identical appearance. Surveillance for cholera episodes was performed at two major hospitals and 11 health facilities across the Dhaka area, with 100% compliance with stool testing for specific markers of cholera diarrhea. Across 6 months of follow-up time, there were 101 first cholera episodes, 37 of which were complicated by severe diarrhea. The 6-month protective efficacy of the oral vaccine was 40% for all cholera episodes (95% [CI], 11% to 60%; p=0.01), and 63% for severely dehydrating cholera episodes (95% [CI], 24% to 82%; p=0.007). The vaccine was not significantly efficacious against all cholera episodes or severely dehydrating cholera episodes in children vaccinated at younger than 5 years of age (p=0.25). The point estimates for vaccine efficacy among persons 5 to 14 years of age and among persons 15 years of age or older were 63% (nonsignificant; 95% [CI], -39 to 90%) and 56% (significant; 95% [CI], 16 to 77%), respectively. Adverse events occurred with similar frequency in both groups. 

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