THURSDAY, Sept. 24 (HealthDay News) -- In an apparent milestone advance, an experimental AIDS vaccine tested on more than 16,000 young adult volunteers in Thailand cut the risk of infection by a third, researchers reported Thursday.
The researchers acknowledged that the protection offered by the vaccine was relatively modest and did not represent a breakthrough. But the trial results marked a significant gain in the so-far frustrating fight against AIDS, which has killed an estimated 32 million people worldwide since it struck more than a quarter century ago.
Experts said the findings should give scientists important insights into HIV, the virus that causes AIDS, and how it attacks the body's immune system, with the ultimate goal of producing a more effective vaccine.
"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," Dr. Anthony S. Fauci, director of the U.S. National Institute of Allergy and Infectious Diseases, one of the trial's sponsors, told The New York Times.
"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."
The World Health Organization and the U.N. agency UNAIDS said the results "instilled new hope" in the field of HIV vaccine research.
The vaccine is a combination of two vaccines that had previously been unsuccessful in clinical trials. When the Thai clinical trial began in 2006, many scientists thought it would also fail.
"I really didn't have high hopes at all that we would see a positive result," Fauci told the Associated Press.
The study, which used strains of HIV common in Thailand, tested the two-vaccine combination in what's called a "prime-boost" approach. The first vaccine primes the immune system to attack HIV and the second one strengthens the response, the AP reported.
The two vaccines are called ALVAC and AIDSVAX. ALVAC contains canarypox -- a bird virus that has been genetically altered so it can't cause disease in humans -- to transport synthetic versions of three HIV genes into the body. AIDSVAX contains a genetically engineered version of a protein on HIV's surface. Because the vaccines aren't made from a whole virus -- either dead or alive -- they can't cause AIDS, according to the AP.
The study was done in Thailand because U.S. Army scientists did key 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, the AP reported.
For the trial, half of the 16,402 volunteers were given six doses of the two vaccines in 2006 and half were given placebos. They then got regular HIV tests for three years. Fifty one of those who got the vaccines became infected compared to 74 who were given placebos, the Times said.
Although the 31 percent reduction in rates of infection was modest, Col. Jerome H. Kim, a doctor who manages the U.S. Army's HIV vaccine program, called the finding statistically significant. And, he added, it's "first evidence that we could have a safe and effective preventive vaccine," AP reported.
The Thais chosen for the study were a cross-section of that country's young adult population, not just high-risk groups like intravenous drug users or sex workers, Kim added.