amfAR, The Foundation for AIDS Research

Policy Implications of Merck’s Recently Halted HIV Vaccine Trials

December 2007—In November, the HIV Vaccine Trial Network released data from two randomized controlled trials of a leading Merck experimental HIV vaccine. These data confirmed that the vaccine candidate was not effective in preventing HIV infection in male vaccine recipients or in reducing viral load in male volunteers who became HIV-positive during the trial, and the trials were halted immediately.

This development caps a particularly difficult year in the field of HIV prevention research. In January 2007, the cellulose sulfate microbicide trial was stopped when more women using the investigational product became infected with HIV than those using a placebo. Another study investigating the use of latex diaphragms as cervical barriers to HIV infection found no additional benefit of this technology.

The continuing challenges in developing effective prevention technologies have raised several questions about HIV prevention research. Some scientists and epidemiologists are calling for a shift away from experimental technologies toward proven methods of preventing HIV transmission, such as condom usage, syringe exchange programs for injecting drug users, and antiretroviral treatment for the prevention of mother-to-child transmission.

Merck and its partners are currently reviewing data from the stopped trials in order to determine why the once-promising investigational product was not efficacious. All study participants have now been informed of which product they received (vaccine candidate or placebo) and have been made aware of the overall study findings. There are still more than 30 vaccine candidates being studied in various phases of clinical trials, but the failed Merck trials may make it more difficult to recruit eligible volunteers for future vaccine studies.

This setback should not lessen the commitment of scientists, funders, advocates, and the community to develop a successful HIV vaccine. An end to the HIV pandemic requires a comprehensive, multi-pronged approach involving effective behavioral interventions, treatment, comprehensive care, and prevention of transmission using multiple technological advances. But HIV prevention research—including research for vaccine development—is not a priority of the U.S. federal government and does not receive adequate funding. Only 11 percent of U.S. federal funding for HIV/AIDS is allocated to research programs. The National Institutes of Health, the country’s leading agency for biomedical research, has also received flat federal funding for the past four years, which fails to keep pace with biomedical inflation and the rising cost of conducting research.

For additional information about Merck’s stopped vaccine trials, see