Now well into the third decade of the pandemic of human immunodeficiency virus (HIV) and AIDS, we have seen dramatic successes in the treatment of HIV infected persons in the United States and many other countries. Yet the pandemic still rages, with 2.7 million new infections in 2007. Indeed, for every infected person who began receiving antiretroviral therapy in 2007, 2.5 people were newly infected with HIV. Historically, vaccines have been among the most effective public health interventions, preventing the spread of viral infections. But an HIV vaccine has thus far been elusive and the quest disappointing and frustrating, prompting some to wonder whether an effective vaccine will ever be added to the HIV-prevention toolbox