A safe, effective and affordable preventive vaccine offers the best long term hope to control the HIV/AIDS pandemic. Its development, however, has encountered a number of unprecedented scientific challenges, including the genetic and antigenic variability of HIV, the lack of information on immunological correlates of protection, and the uncertain predictive value of available animal models. The first phase I trial of an HIV vaccine was conducted in 1987. Since then, more than 30 candidate vaccines have been tested in more than 60 phase I/II trials, involving approximately 10 000 healthy volunteers. The first generation of vaccines is based on envelope antigens,
aimed at inducing neutralizing antibodies. Novel vaccine concepts are being developed with the objective of inducing cell-mediated immunity against structural or regulatory proteins. Most of the trials have been conducted in the United States and Europe, but several trials have also been conducted in developing countries. The first phase III trials, designed to assess the efficacy of the first generation of HIV vaccines (gp120), started in 1998 in the United States and in 1999 in Thailand. Results from these trials will be available within the next 1-2 years. In order to accelerate HIV vaccine development, additional candidate vaccines must be evaluated in parallel in industrialized and developing countries, and that will require intense
international collaboration and coordination. Critical ethical issues need to be carefully considered and addressed in the implementation of these international trials. It is also imperative to start planning now how to use future HIV vaccines, to ensure that they contribute to the overall HIV/AIDS prevention effort.
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