Preparation for a pneumococcal vaccine trial in The Gambia: individual or community randomisation?

In preparation for a large phase-3 trial of pneumococcal polysaccharide/con jugate vaccine among infants in The Gambia, the relative merits of communit y and individual randomisation were considered. The impact of vaccination m ight be enhanced in a community randomised trial if there was a substantial 'herd' effect. This might occur if those vaccinated comprise a substantial proportion of potential transmitters of infection. However, there are few data on the sources of pneumococcal infections in The Gambia and with the h igh degree of mobility of people in The Gambia, it seems unlikely that any herd effect would be strong. In the absence of a herd effect, a community-r andomised trial would have lower power for the mortality end-points compare d to an individually randomised trial of the same size. In addition, a comm unity-randomised trial might not provide sufficient control against potenti al confounders and blinding might be difficult to sustain if the vaccine ha s a strong effect. An individually randomised trial seems a better strategy under the conditions prevailing in The Gambia. (C) 1999 Elsevier Science L td. All rights reserved.