An experimental AIDS vaccine made using two older vaccines has been found lowering the risk of infection by about a third in a sample group of volunteers.
The vaccine is a combination of Sanofi-Pasteur's ALVAC canary pox vaccine and the failed HIV vaccine AIDSVAX, made by a San Francisco company called VaxGen and now owned by the non-profit Global Solutions for Infectious Diseases.
It lowered the risk of HIV infection by 32% among 16,000 Thai volunteers who had no special risk of AIDS infection.
'We had 74 infections in the placebo group and 51 in the vaccine group,' said Dr Jerome Kim, a US Army colonel at the Walter Reed Army Institute of Research in Maryland, who helped lead the trial.
The result, almost completely unexpected, puzzled researchers, who say they cannot figure out why the vaccine combination is working.
It is also a triumph for its supporters, who went ahead with the giant trial of 16,000 heterosexual volunteers despite critics who said it was unethical or a waste of money because the vaccine was so widely expected to have no effect at all.
'Myself, like others, did not think there was a very high chance that this would give any degree of efficacy,' said Dr Anthony Fauci of the US National Institute of Allergy and Infectious Diseases, which helped pay for the study.
'But nonetheless, we went ahead with the trial and it was controversial to go ahead with it.'
Further muddying the waters of the trial result, people who got the vaccine and who became infected anyway had just as much virus in their blood and just as much damage to their immune systems as HIV patients who went unvaccinated.
This means the vaccine helps to prevent infection but does nothing to affect the virus once it is in the body.
'Although the level of protection that we saw was clearly modest, the study is a major scientific advance,' Dr Kim said.
'It is the first evidence that the development of a safe and effective vaccine is possible. Although we don't have all the answers now, it does have important implications for the future of HIV vaccine design.'
Dr Kim stressed that the vaccine may not work in the people
and places where HIV is most common.
'The vaccine was tested in Thailand and it is really specific for the strains that are circulating in Thailand now,' Dr Kim said.
