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Clinical Trial Comes to a Standstill as Vaccine Seems Ineffective

by Medindia Content Team on September 25, 2007 at 7:07 PM
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Clinical Trial Comes to a Standstill as Vaccine Seems Ineffective

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.


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. 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. 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

Source: Kaiser Family Foundation

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