Abstract
BackgroundKilled oral cholera vaccines (OCVs) have been licensed for use in developing countries, but protection conferred by licensed OCVs beyond two years of follow-up has not been demonstrated in randomized, clinical trials.Methods/Principal FindingsWe conducted a cluster-randomized, placebo-controlled trial of a two-dose regimen of a low-cost killed whole cell OCV in residents 1 year of age and older living in 3,933 clusters in Kolkata, India. The primary endpoint was culture-proven Vibrio cholerae O1 diarrhea episodes severe enough to require treatment in a health care facility. Of the 66,900 fully dosed individuals (31,932 vaccinees and 34,968 placebo recipients), 38 vaccinees and 128 placebo-recipients developed cholera during three years of follow-up (protective efficacy 66%; one-sided 95%CI lower bound = 53%, p<0.001). Vaccine protection during the third year of follow-up was 65% (one-sided 95%CI lower bound = 44%, p<0.001). Significant protection was evident in the second year of follow-up in children vaccinated at ages 1–4 years and in the third year in older age groups.Conclusions/SignificanceThe killed whole-cell OCV conferred significant protection that was evident in the second year of follow-up in young children and was sustained for at least three years in older age groups. Continued follow-up will be important to establish the vaccine's duration of protection.Trial RegistrationClinicalTrials.gov NCT00289224.
Highlights
Cholera is a major global public health problem, causing both epidemic and endemic disease
We developed a simpler, inactivated wholecell only oral cholera vaccines (OCVs) that can be produced inexpensively and might be attractive for use in developing countries, as well as for travelers from industrialized countries
We tested this new OCV in a randomized, controlled field trial that enrolled 69,328 individuals aged one year and older living in urban slums of Kolkata, India
Summary
Cholera is a major global public health problem, causing both epidemic and endemic disease. Injectable cholera vaccines have been abandoned as public health tools, modern oral cholera vaccines (OCVs) have been found to be safe and effective [1]. A field trial of BS-WC vaccine in Bangladesh found that a three-dose regimen was safe and conferred high grade (85%) shortterm protection against cholera; protection was clearly evident throughout the first two years of follow-up, but markedly declined in the third year [4]. We conducted a placebo-controlled, randomized trial to assess the safety and protection conferred by a two-dose regimen of the WC-only vaccine against cholera severe enough to warrant solicitation of Efficacy of a Killed Oral Cholera Vaccine. Killed oral cholera vaccines (OCVs) have been licensed for use in developing countries, but protection conferred by licensed OCVs beyond two years of follow-up has not been demonstrated in randomized, clinical trials
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