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The results: New infections occurred in 51 of the 8,197 given vaccine and in 74 of the 8,198 who received dummy shots. That worked out to a 31 percent lower risk of infection for the vaccine group. Two of the infected participants who received the placebo died.
Scientists don't know why the vaccine combo worked. It was the Army's idea to test the combination, said Dr. Donald Francis, a former government scientist who helped identify HIV as the cause of AIDS and now heads the nonprofit that holds the rights to AIDSVAX.
AIDSVAX is aimed at prompting antibodies to HIV. The Sanofi vaccine spurs cells to attack the virus directly. The combo strategy "bridges the two major arms of the immune system," Francis said.
Scientists need to look at blood samples from study participants to understand why some became infected and others were protected.
"With the limited amount of vaccine we have right now, we've got a small number of studies that we could do," Francis said.
Sanofi officials said the same. The company's Dr. Sanjay Gurunathan said a series of studies "that will take a few years" are planned to see if the vaccine can be improved for licensing, and whether new components should be considered to boost effectiveness.
Even AIDS advocates agreed more research was needed.
"We need to take a deep breath and look at all the available evidence from this trial" before urging that this vaccine be used now, said Julie Davids, a spokeswoman for the Community HIV/AIDS Mobilization Project, a New York-based prevention advocacy group.
The study was done in Thailand because U.S. Army scientists did pivotal research in that country when the AIDS epidemic emerged there, isolating virus strains and providing genetic information on them to vaccine makers. The Thai government also strongly supported the idea of doing the study.
Thailand had a burgeoning AIDS problem when the study began. Aggressive prevention efforts have dramatically cut the rates of new infections there, and only 125 infections occurred in the entire study of more than 16,000 people.
Scientists want to know how long the vaccine's protection will last, whether booster shots will be needed, and whether the vaccine helps prevent infection in gay men and injection drug users, since it was tested mostly in heterosexuals in the Thai trial.
The vaccine had no effect on HIV levels in the blood for those who did become infected. That had been another goal of the study -- seeing whether the vaccine could limit damage to the immune system and help keep infected people from developing full-blown AIDS.
That is "one of the most important and intriguing findings of this trial," Fauci said. It suggests the signs scientists have been using to gauge whether a vaccine was actually giving protection may not be valid.
"It is conceivable that we haven't even identified yet" what really shows immunity, which is both "important and humbling" after decades of research, Fauci said.
On the Net:
Vaccine coalition: http://www.avac.org/
Research umbrella group: http://www.hivvaccineenterprise.org/
Government AIDS info:
Copyright 2009 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.
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