Merck last month 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.
The Merck Phase II trials largely involved volunteers in the U.S. and Latin America, and those trials were overseen by a U.S. ethics board. The South African trials began this year and had their own, separate oversight board, the Post reports. Researchers in Soweto, Cape Town, Durban and two other sites in South Africa began contacting the trial volunteers primarily by cell phone text messages with the goal of "unblinding" the trial, or telling each volunteer whether they received the vaccine or a placebo, according to the Post.
Researchers said that the vaccine will not cause infection with HIV but could cause changes in the immune system that might make HIV transmission easier during later exposure to the virus. Researchers plan to tell the roughly 50% of volunteers who received the vaccine that they might have an increased risk of contracting HIV.
According to Mark Feinberg, Merck's vice president for medical affairs, the U.S. ethics oversight board has not decided if it will tell volunteers in the U.S. and Latin America whether they received the vaccine or a placebo. Feinberg said that continuing research could be compromised if volunteers are told whether they received the vaccine or a placebo. He added that volunteers who request that information will be told.
In addition, researchers are counseling all trial volunteers that the vaccine might lead to a possible increased risk of HIV. "Given the complexity of the issue, we feel the best conclusions will be reached when all the data are analyzed in their entirety," Feinberg said. Vaccine researchers are scheduled to meet in Seattle on Nov. 7 to discuss the trial, the Post reports.
Source: Kaiser Family Foundation