out in thousands of volunteers. The following presents a summary of the development of clinical trials with vaccine candidate products. Development of Vaccine Candidate Products Pre-clinical phase: The safety and immunogenicity of the vaccine product are evaluated in animal trials. This phase must always precede clinical trials in human subjects. Clinical phase: Clinical trials will determine the safety, immunogenicity and eventually the effectiveness of the product tested. There are three mandatory phases before a vaccine is licensed by the relevant health authorities: Phase I: Initial trials of safety (innocuity), immunogenicity and dosing in a limited number of volunteers (10 to 30 individuals). These studies usually involve healthy adults at low risk for HIV infection, for periods varying between 6 months and one year; Phase II: Continuation of the safety and immunogenicity trials The vaccine capacity to stimulate certain immunological responses which might indicate possible protection is evaluated in a larger (around 200) number of individuals. Different doses and schedules are tested, as well as different adjuvants. This phase can last from 6 to 24 months; Phase III: In the third and last phase before the possible license for marketing, the efficacy of the vaccine product is tested in a large number of volunteers (thousands of subjects). The number of volunteers will vary inversely to the incidence of infection and/or the expected 14