New evidence suggests that Merck's experimental HIV vaccine was ineffective among some trial participants with a pre-existing immunity to a common cold virus and might have increased their susceptibility to HIV infection, researchers reported Wednesday at an HIV Vaccine Trials Network conference in Seattle, the Washington Post reports. However, the researchers also said that the findings could be a statistical coincidence and that there is insufficient data to determine the full meaning of the findings, the New York Times reports.
Merck in September announced that it had ended its Phase II trial, which began in late 2004 and involved 3,000 HIV-negative volunteers, after its experimental vaccine failed to prevent HIV infection in participants or prove effective in delaying the progression of the virus to AIDS. The trial was stopped by the Data and Safety Monitoring Board, an independent overseer.
Some researchers have theorized that because HIV-positive people who have stronger CD4+ T-cell responses tend to fight the virus better, a vaccine that simulated a T-cell response might be able to control HIV/AIDS. The Merck vaccine was made from a weakened version of a common cold virus that served as a mode for providing three synthetically produced genes from HIV, known as gag, pol and nef. Researchers late last month asked more than 3,000 people who participated in the trial to return to study sites for tests and additional follow-up regarding a possible increased risk of HIV.
According to the Times, conference attendees are debating whether the trial investigators should continue to observe the participants without telling them whether they received the vaccine or a placebo. Researchers in South Africa who were testing the same vaccine have told the 801 participants in the separate trial if they received the vaccine. A recommendation on whether to tell the 3,000 people enrolled in the study in the U.S. and Latin America will be made in about 10 days, Keith Gottesdiener, a Merck vice president, said.
Source: Kaiser Family Foundation