Oral Vaccines for Preventing Cholera

Summary

A Cochrane review [Abstract] 1 included 7 large efficacy trials, 4 small artificial challenge studies, and 29 safety trials . Five variations of a killed whole cell vaccine have been evaluated in large scale efficacy trials (4 trials, n=249 935). The overall vaccine efficacy during the first year was 52% (95% CI 35% to 65%), and during the second year was 62% (95% CI 51% to 62%). Protective efficacy was lower in children aged less than 5 years; 38% (95% CI 20% to 53%) compared to older children and adults; 66% (95% CI 57% to 73%). One trial of a killed whole cell vaccine amongst military recruits demonstrated 86% protective efficacy (95% CI 37% to 97%) in a small epidemic occurring within 4 weeks of the 2-dose schedule (n=1426). Efficacy data is not available beyond two years for the currently available vaccine formulations, but based on data from older trials is unlikely to last beyond three years. The safety data available have not shown any clinically significant increase in adverse events compared to placebo.

A meta-analysis 2 included 7 trials (n=695) and 6 observational studies (n=217), with an average two-dose efficacy of 58% (95% CI 42 to 69, I²=58%) and effectiveness of 76% (95% CI 62 to 85, I²=0). Average two-dose efficacy in children younger than 5 years (30%, 95% CI 15 to 42, I²=0%) was lower than in those 5 years or older (64%, 95% CI 58 to 70, I²=0%; p<0.0001). Two-dose efficacy estimates were similar during the first 2 years after vaccination, with estimates of 56% (95% CI 42 to 66, I²=45%) in the first year and 59% (95% CI 49 to 67, I²=0) in the second year. The efficacy reduced to 39% (13 to 57, I²=48%) in the third year, and 26% (-46 to 63, I²=74%) in the fourth year.