The primary objective of the study is to determine if this vaccine protects individuals from HIV infection. As a secondary objective, the study will investigate whether the vaccine has any impact on HIV viral load on those participants that get infected despite vaccination. Beyond the potential efficacy effect of the vaccine, the VaxGen phase III trial is also being closely watched as a demonstration of industry's capability to successfully conduct these large trials in the U.S. and Asia. It is made of recombinant versions of the HIV surface protein gp120 produced by genetically engineered bacteria. The two B subtype strains used are the MN and the GNE8.
E is the most common subtype in that country.
Of these 1,100 people, about 600 were HIV-negative individuals enrolled in phase I and phase II studies of this product as a preventive vaccine. The rest were HIV-positive individuals who participated in the therapeutic studies of this vaccine. Human phase II studies showed that most participants developed neutralizing antibody responses against viruses of the same strain the vaccine was made from, or other closely related lab-adapted viruses. Both MN and IIIB are considered lab-adapted viruses because they are grown in laboratory cell lines. Breakthrough infections such as these are expected in these initial trials, and they must be carefully interpreted since these studies were not designed to demonstrate efficacy.