Vaccines for preventing cholera.
Graves P., Deeks J., Demicheli V., Pratt M., Jefferson T.
BACKGROUND: Oral cholera vaccines (either killed whole cell or live recombinant vaccines) are newer alternatives to the parenteral vaccines which have been thought to confer only moderate and short-term immunity. OBJECTIVES: The objective of this review was to assess the effect of cholera vaccines in preventing cases of cholera and preventing deaths. SEARCH STRATEGY: We searched the Cochrane Infectious Diseases Group trials register, Medline, Embase and reference lists of articles. We handsearched the journal Vaccine, contacted researchers in the field and manufacturers. SELECTION CRITERIA: Randomised and quasi-randomised studies comparing cholera vaccines (killed or live) with placebo, control vaccines or no intervention, or comparing types, doses or schedules of cholera vaccine. We included adults and children irrespective of immune status or special risk category. DATA COLLECTION AND ANALYSIS: Data extraction and assessment of trial quality was done independently by two reviewers. MAIN RESULTS: Thirty-two trials were included. Seventeen efficacy trials of relatively good quality, testing parenteral and oral killed whole cell vaccines and involving over 2. 6 million adults, children and infants were included. Nineteen safety trials have been conducted for both types of killed whole cell vaccines and for live vaccines and have involved 11,459 people. For all types of vaccines compared to placebo, the relative risk of contracting cholera at 12 months was 0.49, 95% confidence interval 0. 41 to 0.59 (random effects model). This translates to an efficacy of 51%, 95% confidence interval 41% to 59%. Both parenteral and oral administration were relatively efficacious, but significant protection extended into the third year for oral killed whole cell vaccines. Children under 5 were only protected for up to a year, while older children or adults were protected for up to three years. Parenteral killed whole cell vaccines were associated with increased systemic and local adverse effects compared to placebo. Oral killed whole cell vaccines or oral live vaccines were not. REVIEWER'S CONCLUSIONS: Cholera killed whole cell vaccines appear to be relatively effective and safe. Live oral recombinant vaccines appear to be safe, but efficacy data are not available. Protection against cholera appears to persist for up to two years following a single dose of vaccine, and for three to four years with an annual booster.