Earlier this year my colleagues and I carried out a Cochrane review of the effects of cholera vaccines. The review was large, but because of the data available we concentrated mainly on the older killed whole cell (KWC) variety of vaccines. At the beginning of the review we were aware that cholera KWC vaccines have been discouraged since the 1970s in either endemic or epidemic areas on the grounds that they had low efficacy and short duration (four to six months), required multiple doses, and were less effective in children under 5than in adults. Important adverse effects were said to occur in 30% of recipients of injected KWC vaccines. Our Cochrane review re-examined the evidence for these statements through a systematic review of randomised and quasirandomised controlled cholera vaccine trials of over 2.5m participants conducted world wide since 1963.The overall efficacy of vaccine compared with placebo was 57% (95% confidence …