Issues in the design and implementation of vaccine trials in less developed countries.

There is a growing need for vaccine trials in developing countries. This need arises from the fact that some vaccines do not perform as well in developing as in industrialized country populations and because some newly developed candidates target diseases found only in less-developed countries. Here we discuss several key issues in the design and implementation of vaccine trials in less-developed countries. These include the phasing of vaccine trials on safety, immunogenicity and efficacy to achieve licensure; the recent use of trials to obtain other information crucial to the ultimate deployment of vaccines (such as immunological correlates of protection, indirect vaccine effects, and practical information on the feasibility, costs and acceptability of vaccine introduction); and several ethical issues that have arisen in connection with trials done in developing countries.