Vaccine helps prevent HIV infection, new study shows.

Byline: Seattle Times News Services

For the first time, an experimental vaccine has prevented infection with the AIDS virus, a watershed event in the deadly epidemic and a surprising result. Recent failures led many scientists to think such a vaccine might never be possible.

The vaccine, known as RV 144, cut the risk of becoming infected with HIV by more than 31 percent in the world's largest AIDS vaccine trial of more than 16,000 volunteers in Thailand, researchers announced today.

Even though the benefit is modest, "it's the first evidence that we could have a safe and effective preventive vaccine," said Col. Jerome Kim. He helped lead the study for the U.S. Army, which sponsored it with the National Institute of Allergy and Infectious Diseases.

"I don't want to use a word like 'breakthrough,' but I don't think there's any doubt that this is a very important result," said institute's director, Dr. Anthony Fauci.

"For more than 20 years now, vaccine trials have essentially been failures," he said. "Now it's like we were groping down an unlit path, and a door has been opened. We can start asking some very important questions."

Even a marginally helpful vaccine could have a big impact. Every day, 7,500 people worldwide are newly infected with HIV; 2 million died of AIDS in 2007, the U.N. agency UNAIDS estimates.

"Today marks a historic milestone," said Mitchell Warren, executive director of the AIDS Vaccine Advocacy Coalition, an international group that has worked toward developing a vaccine.

"It will take time and resources to fully analyze and understand the data, but there is little doubt that this finding will energize and redirect the AIDS vaccine field," he said.

The Thailand Ministry of Public Health conducted the study, which used strains of HIV common in Thailand. It is not known if a such a vaccine would work against other strains, scientists said.

The study actually tested a two-vaccine combo in a "prime-boost" approach, where the first one primes the immune system to attack HIV and the second one strengthens the response.

They are ALVAC, from Sanofi Pasteur, the vaccine division of French drugmaker Sanofi-Aventis; and AIDSVAX, originally developed by VaxGen and now held by Global Solutions for Infectious Diseases, a nonprofit founded by some ex-VaxGen employees.

ALVAC uses canarypox to ferry synthetic versions of three HIV genes into the body. AIDSVAX contains a genetically engineered version of a protein on HIV's surface. The vaccines are not made from whole virus -- dead or alive -- and cannot cause HIV.

Neither vaccine prevented HIV infection when tested individually in earlier trials.

But "the combination is stronger than each of the individual members," the Army's Kim said.

The study tested the combo in HIV-negative Thai men and women at average risk of becoming infected. Half received four "priming" doses of ALVAC and two "boost" doses of AIDSVAX over six months. The others received dummy shots. They were followed for three years.

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.

The vaccine had no effect on levels of HIV in the blood of 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 result is "one of the most important and intriguing findings of this trial," Fauci said. It suggests that 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" after decades of vaccine research, Fauci said.

Compiled from The Associated Press and The New York Times reports.

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