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This chapter emphasizes the global molecular epidemiology of human immunodeficiency virus (HIV) including an overview of its genetic diversity and related implications. Advances in molecular biology, immunology, and epidemiology have contributed greatly to the understanding of HIV. HIV is a primate retrovirus that shares the ability to infect their host chronically and progressively damage the host's immune system. Genetic variation of HIV is extremely high as a consequence of the rapid turnover of HIV virions. Individuals infected with HIV maintain a substantial viral burden during the entire course of infection. Related strains share genetic similarity, as expressed by the sequence of component nucleotides and methods have been developed to infer the phylogenetic relationships among different strains. Furthermore, at present, data regarding HIV subtypes is mostly limited to studies conducted for purposes other than surveillance. The expansion of epidemiologic surveillance for different strains of HIV and attempts to collect representative specimens from different populations can provide useful information to the public health community on the danger of emerging infectious agents such as HIV.

This chapter describes obstacles hindering the development of a preventive human immunodeficiency virus (HIV) vaccine, progress toward developing and evaluating vaccine candidates, clinical trials, the social and ethical issues involved in conducting HIV vaccine trials, and plans for future efficacy trials. Three obstacles are widely considered responsible for hindering the development of an HIV-1 vaccine. These obstacles are the extensive antigenic variability of HIV, uncertainty regarding which immune responses are correlated with protection, and the lack of an ideal animal model on which to test vaccine constructs. Despite the difficulties involved in developing an HIV vaccine, more than 80 vaccine constructs have proceeded to human clinical trials and one of two large-scale efficacy trials has been completed, with the second scheduled for completion by late 2003. Furthermore, there is an increasing awareness among trial investigators regarding the ethical and social obligations to protect trial participants' rights and provide important human rights protections.