An experimental AIDS vaccine made from two older versions has protected people for the first time, reducing the rate of infection by about 30 per cent, researchers said today.
Developers said they were now debating how to test the limited amounts of vaccine they have left to find out if there are ways to make it better.
Scientists said they are unsure how or why the vaccines worked and will study the volunteers in the trial to find out.
Both agreed the vaccine's immediate usefulness may be limited and a commercial vaccine would be years away.
"The result of the study is a very important step for developing an AIDS vaccine," Thai Health Minister Withaya Kaewparadai said.
"It's the first time in the world that we have found a vaccine that can prevent HIV infection."
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 nonprofit Global Solutions for Infectious Diseases.
The trial was sponsored by the US government and conducted by the Thai Ministry of Public Health.
Officials from the two countries told a news conference in Bangkok the risk of infection had been cut by 31.2 per cent among 16,402 volunteers.
Reuters