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AIDS Vaccine Success Is 'Modest'

First-Ever Protective Effect Is Small but Suggests HIV Vaccine Is Possible
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WebMD Health News
Reviewed by Louise Chang, MD

Sept. 24, 2009 - "Modest" success in an HIV vaccine trial shows for the first time that vaccination can protect people against infection with the AIDS virus.

It's a small but significant step forward. Few, if any, think this vaccine is effective enough to deploy in the worldwide fight against AIDS. But many experts say it offers badly needed hope to an effort marked by many expensive failures.

"While these results are encouraging, we recognize that further study is required to build upon these findings," Col. Nelson Michael, director of the U.S. Military HIV Research Program, says in a news release.

The trial was a collaboration between the U.S. Army, Thailand, the U.S. National Institute of Allergy and Infectious Diseases, Sanofi Pasteur, and Global Solutions for Infectious Diseases. It tested Sanofi's ALVAC vaccine boosted with a dose of GSID's AIDSVAX.

Conducted in Thailand, it began in 2003 and enrolled 16,402 adult, HIV-negative men and women. Half got the two-part vaccine, and half got inactive placebo shots.

Over the course of the study, 74 placebo recipients and 51 vaccine recipients became infected with HIV. The difference isn't large, but it translates into 31% vaccine effectiveness. That is, it lowered the risk of getting HIV by 31%.

That's "an important step forward in HIV vaccine research," NIAID director and long-time AIDS researcher Anthony Fauci, MD, says in a news release. "Certainly this is an encouraging advance."

Even so, the study results are puzzling. It was expected that vaccine recipients who became infected would at least have some protection against the virus. But the study found no evidence of such protection. HIV levels were just as high in vaccine recipients who became infected as in placebo recipients who contracted the virus.

Perhaps more importantly, the study fell far short of its goal of reducing the risk of HIV infection by 50%.

The study was controversial from the outset. It's the largest HIV vaccine trial yet conducted, and some AIDS activists called the study a waste of precious resources.

AIDSVAX, the first HIV vaccine ever to be tested, had already failed to prevent HIV in a number of trials. ALVAC, a live canarypox virus carrying HIV genes, did not appear to stimulate strong immune responses in healthy people. And similar combination vaccine strategies showed little evidence of eliciting strong immune responses.

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