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HIV Vaccine Success May Take Decade to Unravel Why it Works

September 29, 2009

Last week's startling good news from an HIV vaccine trial in Thailand raises many questions about why the shots reduced HIV infection risk by 31 percent compared with a placebo. [The details of the experiment were summarized in CDC Prevention News Update on Sept. 24].

The theory was that the Sanofi-Aventis' experimental ALVAC vaccine would "prime" the cellular immune system, while Global Solutions for Infectious Diseases' AIDSVAX containing the HIV protein gp120 would "boost" the body's HIV antibody response. AIDSVAX alone failed to show protection in previous tests. In the recent trial, the viral levels among those infected were similar for both subjects who received the vaccine combination and those who got the placebo.

"Some of our preconceived notions about what to measure and what we think is important might have just been turned on its head," said Col. Nelson L. Michael, director of the retrovirology division at Walter Reed Army Medical Center in Washington.

Researchers have not identified antibodies responsible for the success seen in the combination trial, and previous attempts to elicit such antibodies have failed, said Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases.

The trial "tells us that we don't even know what the correlates of immunity are," Fauci said. "But it does give us now a bit more direction for trying to track down what it is this vaccine did that led to this modest degree of protection." "We're not even close to being finished," he added.

"The samples and specimens collected from this trial have become a precious resource," said Mitchell Warren, executive director of the AIDS Vaccine Advocacy Coalition in New York. "Over the next few months we'll see some consensus as to what are the elements of trials that need to be conducted with the current samples."

"You start from nowhere," said Michel Kazatchkine, executive director of the Global Fund to Fight AIDS, TB and Malaria. "Is it one of the components? Is it the mixture? Is it the way it was administered? We need to build more science, more pilot trials, and then one day, another big trial."

Back to other news for September 2009

Adapted from:
Bloomberg News
09.28.2009; Tom Randall

This article was provided by CDC National Prevention Information Network. It is a part of the publication CDC HIV/Hepatitis/STD/TB Prevention News Update.
See Also
HIV/AIDS Vaccine Is Found to Be Partly Effective at Preventing HIV Infection, but Advocates Express Skepticism
Investigational Vaccine Shows Modest Potential for Protecting Against HIV Infection
Basic Information on the RV144 Phase III HIV Vaccine Trial
HIV Vaccine Study First to Show Some Effectiveness in Preventing HIV (Press Release From U.S. Military HIV Research Program)
AIDS Vaccine Results: Thai Trial


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