TRENTON, N.J. -- A promising experimental vaccine to prevent the AIDS virus has failed in a crucial experiment, with volunteers becoming infected with HIV anyway, leading the drug developer to halt the study.
Merck & Co. said Friday that it is ending enrollment and vaccination of volunteers in the large international study, which is partly funded by the National Institutes of Health.
It was a significant setback in the daunting quest to develop a vaccine to prevent AIDS. Merck's vaccine was the farthest along and was closely watched by experts in the field.
Officials at the New Jersey-based company told The Associated Press that 3.2 percent, or 24 of 741 of those who got the vaccine got HIV; 2.8 percent, or 21 of 762 of those on a placebo got it.
"It's very disappointing news," said Keith Gottesdiener, head of Merck's clinical infectious disease and vaccine research group. "A major effort to develop a vaccine for HIV really did not deliver on the promise."
Michael Zwick, an HIV researcher at Scripps Research Institute, said the vaccine's failure is unfortunate. But he said it's too soon to know if other vaccines using the same strategy would also fail.
"It's par for the course in the HIV field," he said of the Merck result.
The volunteers in the experiment were all free of HIV at the start. But they were at high risk for getting the virus: Most were homosexual men or female sex workers. They were all repeatedly counseled about how to reduce their risk of HIV infections, including use of condoms, according to Merck.
In a statement, the NIH said a data safety monitoring board, reviewing interim results, found the vaccine did not prevent HIV infection. Nor did it limit severity of the disease "in those who become infected with HIV as a result of their own behaviors that exposed them to the virus" - another goal of the study.
Merck's was the first major test of a new strategy to prevent HIV infection. The first wave of attempts to develop a vaccine tried to stimulate antibodies against the virus, but that didn't work.
The new effort - an approach that Gottesdiener said is being tried in most other current research - is aimed at making the body produce more of a crucial immune cell called killer T-cells. The goal is to simultaneously "train" those cells, like an army, to quickly recognize and destroy the AIDS virus when it enters cells in the bloodstream.
Zwick said some researchers still are working on vaccines to neutralize the AIDS virus. He thinks ultimately what's needed is one that combines that approach with a way to stimulate and train killer T-cells.
Merck and the HIV Vaccine Trials Network, an international collaboration of researchers and institutions funded by the NIH, co-sponsored the study. The experiment, called STEP, began in December 2004 and had enrolled 3,000 volunteers in Australia, Brazil, Canada, the Dominican Republic, Haiti, Jamaica, Peru, Puerto Rico and the United States.
The Merck vaccine failure is a "deep disappointment and a scientific setback for the AIDS vaccine field," the AIDS Vaccine Advocacy Coalition said in a statement. However, the nonprofit group added that "while this is a disappointment, it is in no way the end of the search for an AIDS vaccine."
Merck & Co. said Friday that it is ending enrollment and vaccination of volunteers in the large international study, which is partly funded by the National Institutes of Health.
It was a significant setback in the daunting quest to develop a vaccine to prevent AIDS. Merck's vaccine was the farthest along and was closely watched by experts in the field.
Officials at the New Jersey-based company told The Associated Press that 3.2 percent, or 24 of 741 of those who got the vaccine got HIV; 2.8 percent, or 21 of 762 of those on a placebo got it.
"It's very disappointing news," said Keith Gottesdiener, head of Merck's clinical infectious disease and vaccine research group. "A major effort to develop a vaccine for HIV really did not deliver on the promise."
Michael Zwick, an HIV researcher at Scripps Research Institute, said the vaccine's failure is unfortunate. But he said it's too soon to know if other vaccines using the same strategy would also fail.
"It's par for the course in the HIV field," he said of the Merck result.
The volunteers in the experiment were all free of HIV at the start. But they were at high risk for getting the virus: Most were homosexual men or female sex workers. They were all repeatedly counseled about how to reduce their risk of HIV infections, including use of condoms, according to Merck.
In a statement, the NIH said a data safety monitoring board, reviewing interim results, found the vaccine did not prevent HIV infection. Nor did it limit severity of the disease "in those who become infected with HIV as a result of their own behaviors that exposed them to the virus" - another goal of the study.
Merck's was the first major test of a new strategy to prevent HIV infection. The first wave of attempts to develop a vaccine tried to stimulate antibodies against the virus, but that didn't work.
The new effort - an approach that Gottesdiener said is being tried in most other current research - is aimed at making the body produce more of a crucial immune cell called killer T-cells. The goal is to simultaneously "train" those cells, like an army, to quickly recognize and destroy the AIDS virus when it enters cells in the bloodstream.
Zwick said some researchers still are working on vaccines to neutralize the AIDS virus. He thinks ultimately what's needed is one that combines that approach with a way to stimulate and train killer T-cells.
Merck and the HIV Vaccine Trials Network, an international collaboration of researchers and institutions funded by the NIH, co-sponsored the study. The experiment, called STEP, began in December 2004 and had enrolled 3,000 volunteers in Australia, Brazil, Canada, the Dominican Republic, Haiti, Jamaica, Peru, Puerto Rico and the United States.
The Merck vaccine failure is a "deep disappointment and a scientific setback for the AIDS vaccine field," the AIDS Vaccine Advocacy Coalition said in a statement. However, the nonprofit group added that "while this is a disappointment, it is in no way the end of the search for an AIDS vaccine."
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