An experimental AIDS vaccine tested in Thailand on some 2,500 drug users failed to protect them from becoming infected with HIV, the vaccine's developer said Wednesday.
The poor results were widely expected since VaxGen Inc. had said earlier that its vaccine did not work in a larger North American study.
Most AIDS researchers agree that vaccines will be the only effective way to control a virus that has killed 28 million people and infected 42 million more worldwide.
Two-dozen other vaccines are being tested on 12,000 human volunteers, but none has advanced as far as VaxGen's, and any successful candidate is years away.
Officials at Brisbane, Calif.-based VaxGen said the Thai results underscored again how wily AIDS is in thwarting the immune system.
The findings also show "how important it is for the international public health community to redouble the effort to develop an effective vaccine," president Dr. Donald Francis said.
VaxGen's vaccine, like most others being tested, did not contain the virus itself and cannot cause AIDS. Instead, the vaccine contained small, manmade genetic bits of the virus that scientists had hoped would provoke an immune response strong enough to stop the virus from invading healthy cells.
Three years ago, the company enrolled 2,546 people in and around Bangkok who were at high risk for HIV because they habitually swapped needles to inject drugs. Half were given the experimental vaccine and half were given a placebo. All volunteers were given extensive risk-reduction counseling, the company said.
In the end, the vaccine offered no greater protection: 105 people given the placebo became infected with HIV, while 106 people given the vaccine tested positive.
In February, VaxGen announced its vaccine was ineffective against a different AIDS strain found in North America. In that experiment, the vaccine failed in a test with 5,400 volunteers at risk because of their sexual habits.