Oral cholera vaccine moderately effective in reducing the burden of severely dehydrating diarrhea

1. In this cluster-randomized, open-label trial, a whole-cell cholera vaccine demonstrated moderate effectiveness of around 40% in protecting against severely dehydrating cholera.

2. The vaccine was well tolerated with no reported vaccine-related serious adverse events. Behavioral change had a small augmenting effect to the vaccine efficacy.

Evidence Rating Level: 1 (Excellent)

Study Rundown: Cholera is a diarrheal disease that can cause severe dehydration, and as such poses a significant threat in low-income countries. This randomized, open-label study assessed the effectiveness and feasibility of oral cholera vaccine against severely dehydrating cholera in a real-life urban setting through government services in Bangladesh. Participants were assigned to a vaccination-only group, a vaccination and behavioral intervention group, or a no-intervention group. The vaccination-only group received 2 standard doses of oral cholera vaccine and the vaccination and behavioral intervention group received 2 standard doses of vaccine and additionally participated in a program promoting hand-washing and drinking water treatment with chlorine. The primary outcome for this study was protective effectiveness against severely dehydrating cholera during 2-year follow up. Overall protective effectiveness was 37% in the vaccination only group and 45% in the vaccination and behavioral change group. A strength of this study is that it demonstrated effectiveness in real life application with a large trial population. A potential weakness is that a placebo was not used in the control group and thereby prevented masking of the study.

The study was funded by Bill & Melinda Gates Foundation.

Click to read the study in The Lancet

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

In-Depth [randomized controlled trial]: This cluster-randomized open-label trial aimed to analyze the acceptability, programmatic feasibility, and protective effectiveness of oral cholera vaccine against severely dehydrating cholera in an urban setting in Bangladesh with high rates of cholera. 267,270 participants were randomly assigned (1:1:1) to either a vaccination-only group that received 2 standard doses of oral cholera vaccine, a vaccination and behavioral intervention group that received 2 standard doses of the vaccine, plus participating in a program promoting hand-washing and drinking water treatment with chlorine, or a no-intervention group.

The primary outcome was protective effectiveness against severely dehydrating cholera during 2-year follow up for all individuals present after the second dose. Vaccine coverage was 65% in the vaccination-only group and 66% in the vaccination and behavioral intervention group. Overall, protective effectiveness was 37% (95% CI lower bound 18%; p=0.0024) for the vaccine-only group and 45% (95% CI lower bound 24%; p=0.0011) in the vaccination and behavioral intervention group. The occurrence of cholera was not significantly between the vaccination-only group and the vaccination and behavioral change group (p=0.50). The vaccine showed no protection against enterotoxigenic E coli diarrhea (protective effectiveness 1%, 95% CI lower bound -23%; p=0.46). There were no reported serious adverse events. Most common non-serious adverse events included acute watery diarrhea, vomiting, abdominal pain, and fever.

Image: PD

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