Researchers have asked more than 3,000 people who participated in a trial of Merck's experimental HIV vaccine that was halted last month to undergo additional testing to determine if they are at an increased risk of HIV, Reuters reports (Fox, Reuters, 10/25).
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 (Kaiser Daily HIV/AIDS Report, 10/25).
Researchers said that they do not have enough information to determine whether the participants who received the vaccine are more susceptible to HIV but that initial information is worrisome. Officials from Merck and NIH's National Institute of Allergy and Infectious Diseases emphasized that the vaccine could not result in HIV infection because it contains three synthetically produced genes that have "no way" to "reconstitute an intact virus."
According to NIAID, which co-sponsored the trial, researchers are "analyzing available data to better understand if there may be an increased susceptibility to acquiring HIV infection among those volunteers who received the vaccine." Mark Feinberg, Merck's vice president for medical affairs and public health, in an e-mail said that researchers are analyzing a "tremendous amount of data."