Vaccines for preventing cholera.

BACKGROUND

Oral cholera 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

Twenty-five trials were included. Eighteen 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. No randomised efficacy trials of live vaccines were available and therefore this review is restricted to killed vaccines only. Eleven safety trials have been conducted for both types of killed whole cell vaccines and have involved 9,342 people. For killed whole cell 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, while oral killed whole cell vaccines were not.

REVIEWER'S CONCLUSIONS: Cholera killed whole cell vaccines appear to be relatively effective and safe. 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.