There are many possible outcomes of HIV-1 infection among persons who receive experimental HIV-1 vaccines. In the best-case scenario, these vaccines may prevent infection (sterilizing immunity). However, current viral vaccines are thought to limit, but not prevent, virus replication after infection. In the latter case, it is important to document the effect of the immune response on the disease course as reflected by viral load, the evolution of the viral quasi species, and clinical symptoms over time. Understanding the evolution of the immune response in vaccinees after subsequent exposure and HIV infection will potentially result in valuable information for the subsequent design of preventive and therapeutic vaccines. This will be studied here using HIVNET 014 participants at higher risk for HIV-1 infection.