Merck Halts International HIV Vaccine Trial

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HIV Vaccine Trial

Merck on Fridayannounced that it has halted a large-scale clinical trial of itsexperimental HIV vaccine after the drug failed to prevent HIV infectionin participants or prove effective in delaying the progression of thevirus 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 mostpromising to be tested on people so far." Some researchers havetheorized that because HIV-positive people who have stronger T-cellresponses tend to fight the virus better, a vaccine that simulated aT-cell response might be able to control HIV/AIDS, the Timesreports. The Merck vaccine was made from a weakened version of a commoncold virus that served as a mode for providing three syntheticallyproduced genes from HIV, known as gag, pol and nef. It showed "enoughpromise" in animal trials and small human tests to conduct alarge-scale trial, the Times reports.



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

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! News, 9/22). According to the San Francisco Chronicle,one factor that might distinguish the South African trial is that it isbeing conducted against a different subtype of HIV that is predominantin the country (Russell, San Francisco Chronicle, 9/22).


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

Some researcherswarned against "overreacting" to the outcome of the trial becausevarious types of vaccines are known to stimulate different kinds ofimmunity, 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 resultswill have to be reviewed before approving a new trial set to begin inJanuary 2008 that will seek to stimulate an immune response amongT-cells, in addition to stimulating antibodies against the virus (San Francisco Chronicle, 9/22).

Reprinted with permission from You can view theentire Kaiser DailyHIV/AIDS Report, search the archives, and sign up for email delivery at . TheKaiser Daily HIV/AIDS Report is published for, a free service ofThe Henry J. Kaiser Family Foundation.