based on our present knowledge, it is possible that several vaccines (or true “cocktails”) are required to deal with the various HIV subtypes prevalent in the different countries affected by the epidemic. In spite of these difficulties, the scientific community is reservedly optimistic concerning the possibility of developing one or more vaccines with varying levels of effectiveness against HIV. This optimism is based on several facts, including: a) the existence of individuals who are repeatedly exposed to HIV, do not become infected and develop immunological responses which might explain this resistance; others probably do not become infected because of the lack or changes in the receptors required for HIV entry in the cells; b) the existence of vaccine products that protect monkeys from the infection or from developing the disease ; c) some vaccine products have triggered potent immunological reactions in human volunteers; d) the successful development of other vaccines against several viruses (e.g., hepatitis, poliomyelitis, mumps) even when the understanding of pathophysiology was smaller than in the case of HIV infection. Vaccine candidates and need for involvement in HIV research, development and evaluation There are three different types (and purposes) of vaccine candidate products being developed and evaluated: 1. Preventive vaccines: to prevent HIV infection (sterilizing immunity) or the progress towards AIDS (partial immunity); 11