THURSDAY, Sept. 24, 2009 (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.
One curious finding showed that the vaccine induced very few antibodies. Most vaccines consist of parts of a virus or bacterium that prompt the immune system to make antibodies, which then protect the body by attacking the invading pathogen.
The chief usefulness of the ALVAC-AIDSVAX vaccine will probably be what it can teach infectious-disease researchers about what is happening in the immune system when a person is even somewhat protected against HIV, the Washington Post reported.
"We really need to go through the data to see if there are effects here that are potentially useful," Kim said.
He predicted that information gained from the trial after the results are fully analyzed will have "important implications for the design of future HIV vaccines," the Post reported.
Fauci stressed that the new trial results do not mark "the end of the road," but he was surprised and pleased by the outcome, the AP reported.
"It gives me cautious optimism about the possibility of improving this result" and developing a more effective AIDS vaccine, he said. "This is something that we can do."
Leaders in the search for an AIDS vaccine were also heartened by the news.
Dr. Alan Bernstein, executive director of the Global HIV Vaccine Enterprise in New York City, said, "The results themselves are modest: 30 percent protection is not a level of protection that we can actually go out and give to people, but it's a landmark day because it says that achieving protection in humans against HIV with an HIV vaccine is possible."
"It's going to be so exciting over the next few years to go from 30 percent protection to 100 percent protection," he added.
Rowena Johnston, director of research for the Foundation for AIDS Research, New York City, added, "This is an important step, it's an encouraging step, but it is not the final step."
"These results are interesting from the perspective of what we are going to learn out of them," she said. "There are probably few people who would say this is the product we should be making available to people around the world. But it is showing us directions in which we might look."
Seth Berkley, president and chief executive officer of the International AIDS Vaccine Initiative, said in a prepared statement: "It's the first demonstration that a candidate AIDS vaccine provides benefit in humans. Until now, we've had evidence of feasibility for an AIDS vaccine in animal models. Now, we've got a vaccine candidate that appears to show a protective effect in humans, albeit partially."
In 2007, 33 million people around the world were living with HIV/AIDS. More than 64.9 million people have been infected with HIV since the pandemic began. AIDS is the leading cause of death in sub-Saharan Africa, and the fourth leading cause of death globally, according to the U.S. Agency for International Development.
ALVAC is made by Sanofi Pasteur, the vaccine division of French drugmaker Sanofi-Aventis. AIDSVAX was originally developed by VaxGen Inc., and the patent is now held by Global Solutions for Infectious Diseases, a nonprofit group founded by some former VaxGen employees, AP reported.
In addition to the two vaccine patent holders and the U.S. National Institute of Allergy and Infectious Diseases, participants in the Thai trial included the United States Army, and the Thai Ministry of Public Health, the Times reported.
More information on the trial will be presented at an AIDS vaccine meeting in Paris later this fall, the Post reported.
To learn more about HIV and AIDS, visit the U.S. Centers for Disease Control and Prevention.