Merck began research into an HIV vaccine shortly after the virus was identified in the mid-1980s and has been actively involved in HIV vaccine R&D since that time.

Merck’s research effort has targeted both antibody-based and cellular-immune-based vaccine approaches to preventing HIV infection. In 2005, Merck and its partners began a large trial to test the efficacy of a Merck developmental cellular-immune-based vaccine. The study, known as the STEP trial, was cosponsored with the National Institutes of Health (NIH) and the HIV Vaccine Trials Network (HVTN) and designed to evaluate whether the vaccine prevented HIV infection; and whether the vaccine reduced virus levels in those who developed infection. In an interim analysis, the vaccine did not reduce the incidence of infection nor did it reduce virus levels.

In September 2007, Merck announced that its vaccination in a Phase II clinical trial of the company’s investigational HIV vaccine (V520) was being discontinued because the vaccine was not effective.

Merck continues to work with the research community to understand the study results of the STEP trial and its implications for the field of AIDS-vaccine R&D. Merck scientists continue to research antibody-based approaches and have been studying novel immunogen designs based on essential and conserved regions of the HIV envelope glycoprotein. Merck has recently established collaborative research projects with academic investigators to advance promising antibody-based approaches for an HIV-1 vaccine.