Experts are calling an experimental AIDS vaccine an "encouraging" breakthrough in the fight against the disease, but say it is far from being a silver bullet.
A study testing a new vaccine on more than 16,000 volunteers in Thailand found that the series of shots cut the risk of becoming infected with HIV, the virus that causes AIDS, by more than 31 per cent.
"It's the first time in the world that we have found a vaccine that can prevent HIV infection," Thai health minister Withaya Kaewparadai said Thursday.
But less than a third is not a major degree of protection. Years of further study will be needed to ensure the vaccine is safe and effective enough to be made available to the public.
"Thirty per cent is not enough to say we can go launch a vaccine," said Chris Viehbaker, CEO of Sanofi-Pasteur. "But when you look at everything that has been done over the last 10 years, every vaccine project up until now has failed."
Three years after the vaccinations in the Thai study ended, there were 51 new infections among the half who were given the vaccine, compared to 74 infections among the half who received a placebo.
Study participants were injected with a combination of two older vaccines that were found to not work on their own. The first was Sanofi-Pasteur's ALVAC canary pox vaccine. The second was AIDSVAX, made by a San Francisco company called VaxGen and now owned by the nonprofit Global Solutions for Infectious Diseases.
The volunteers who didn't get the placebo were given six immunizations over six months, four with ALVAC and two with AIDSVAX.
The combo had been widely expected to have no effect, so the results surprised and delighted the researchers, who said they still don't understand why the combination worked.
All the volunteers, who were HIV negative men and women aged 18 to 30 at average risk of becoming infected, were given condoms and counseling and were tested every six months for HIV. Anybody who became infected was given free treatment with antiviral medicines.
The ALVAC vaccine was meant to prime the immune system to attack HIV, by using a bird virus to carry synthetic versions of three HIV genes into the body. AIDSVAX then strengthened the immune response by introducing a genetically engineered version of a protein on HIV's surface.
The vaccines were not made from the real HIV virus -- dead or alive -- and could not cause HIV.
But the researchers caution that the effectiveness of the vaccine may be limited because there are many strains of HIV now in circulation around the world.
This study used strains of HIV common in Thailand, so whether it will work against other strains in the U.S., Africa or elsewhere in the world is unknown.
The US$105 million study was sponsored by the U.S. army and conducted by the Thai Ministry of Public Health. Officials from the two countries told a news conference in Bangkok that the study's findings are "a very important step for developing an AIDS vaccine."
Dr. Anthony Fauci of the U.S. National Institute of Allergy and Infectious Diseases, which helped fund the study, admitted he was one of those who didn't think the vaccine would work.
"Myself, like others, did not think there was a very high chance that this would give any degree of efficacy," he said. "But nonetheless, we went ahead with the trial and it was controversial to go ahead with it."
Fauci said there was still more work to be done, but these initial findings give him cautious hope that they can develop a more effective AIDS vaccine.
As well, the researchers were surprised by a finding among the people who got the vaccine and who became infected anyway. They had hoped that the vaccine would at least help keep infected people from developing full-blown AIDS.
But they found the infected and vaccinated group had just as much virus in their blood and just as much damage to their immune systems as HIV patients who went unvaccinated. That meant the vaccine did nothing to affect the virus once it is in the body.
The World Health Organization and the U.N. agency the Joint United Nationals Programme on HIV/AIDS (UNAIDS), said the findings gave "new hope" in battling the disease.
"The study results, representing a significant scientific advance, are the first demonstration that a vaccine can prevent HIV infection in a general adult population and are of great importance," UNAIDS said in a statement.
Every day, 7,500 people worldwide are newly infected with HIV. Two million people died of AIDS in 2007, UNAIDS estimates.
With files from The Associated Press
