Roughly 7,500 healthy people will be picked for the three-year $20m (pounds 12m) study, which is due to begin shortly. If it is successful, a vaccine could be publicly available early next century.
While some 40 potential vaccines have been developed by US researchers, most have been disappointing and only one has made it to phase II testing. This is the first time approval has been given for a fully fledged phase III study. While phase II studies are designed to evaluate the safety of a vaccine, it is only at phase III that effectiveness is properly judged.
The company, VaxGen, said about 5,000 of the participants will be in the US with another 2,500 recruited in Thailand. About half the individuals, who will be healthy but at high risk of HIV infection, will receive the vaccine while the others will be injected with a placebo.
"There's nothing magic about this vaccine, but it's our best hope so far and it's time to take the next step," Donald Francis, president of VaxGen, is reported as saying. "I am optimistic".
The reaction in the Aids advocacy community, which has suffered so many disappointments, was cautious. "The vaccine is not the end of the road. It is the beginning," said Jose Zuniga of the International Association of Physicians in Aids Care.
The key ingredient of the experimental vaccine, which has been under development for a decade, is a protein named gp120, which should bind together the Aids virus in the body. In theory, it will help create antibodies that would prevent the virus from attaching to receptors on white blood cells.
- David Usborne, New YorkReuse content