Merck Halts International HIV Vaccine Trial

Merck on Friday announced that it has halted a large-scale clinical trial of its experimental HIV vaccine after the drug failed to prevent HIV infection in participants or prove effective in delaying the progression of the virus to AIDS, the Wall Street Journal reports. The trial was stopped Tuesday by the Data and Safety Monitoring Board, an independent overseer, the Journal reports (Chase/Schoofs, Wall Street Journal, 9/22).

According to the New York Times, experts had considered the experimental vaccine "one of the most promising to be tested on people so far." Some researchers have theorized that because HIV-positive people who have stronger 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 Times reports. 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. It showed "enough promise" in animal trials and small human tests to conduct a large-scale trial, the Times reports.

The Phase II trial, which began in late 2004, involved 3,000 HIV-negative volunteers, largely in the U.S. and Latin America. Participants received three doses of the vaccine during a six-month period. Results of the trial were not expected until the end of 2008 at the earliest, according to the Times. However, the first scheduled interim analysis of 1,500 volunteers found that of the 741 people who received at least one dose of the vaccine, 24 HIV cases were found after volunteers had been followed for about 13 months. Those results were compared with 21 HIV cases among 762 people who were given a placebo. The vaccine also did not reduce HIV viral loads in participants who contracted HIV during the trial, according to the analysis.

The board advised the trial's investigators -- led by Lawrence Corey of the University of Washington and the Fred Hutchinson Cancer Research Center -- to stop vaccinations but to continue monitoring study participants, according to the Times (Altman/Pollack, New York Times, 9/22). Merck also temporarily stopped vaccinations in another trial in South Africa, AFP/Yahoo! News reports. The vaccine had been tested on 700 HIV-negative people since February in five South African hospitals (AFP/_Yahoo! New_s, 9/22). According to the San Francisco Chronicle, one factor that might distinguish the South African trial is that it is being conducted against a different subtype of HIV that is predominant in the country (Russell, San Francisco Chronicle, 9/22).

"Given that this study was the leading edge" of research on T-cell-based HIV vaccines, "there was great disappointment" in halting the trial, Mark Feinberg, vice president for medical affairs and health policy in Merck's vaccine division, said, adding, "There is nothing on the horizon" at Merck. "We don't have any other vaccine candidates we've identified as promising enough to advance into clinical studies," he said, adding that the company is "committed to finding ways to share information accumulated over two decades to facilitate the broader effort" to develop an HIV vaccine (Wall Street Journal, 9/22). "It is devastating for us, to say the least, but we have to keep going ... we need something that can prevent infection," South African trials supervisor Glenda Gray said. She added that the prototype did not have any consequence on the health of those who participated in the study (AFP/Yahoo! News, 9/22).

Some researchers warned against "overreacting" to the outcome of the trial because various types of vaccines are known to stimulate different kinds of immunity, the Journal reports. "It isn't the end of the line," Mitchell Warren, executive director of the AIDS Vaccine Advocacy Coalition, said, adding that Merck's data "aren't the answers we wanted but they will help improve our other vaccine candidates" (Wall Street Journal, 9/22). Anthony Fauci, director of NIH's National Institute of Allergy and Infectious Diseases, said, "This is sobering, if not disturbing news," adding the results will have to be reviewed before approving a new trial set to begin in January 2008 that will seek to stimulate an immune response among T-cells, in addition to stimulating antibodies against the virus (San Francisco Chronicle, 9/22).

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