Leading AIDS researchers said they were more optimistic than ever about developing a vaccine capable of controlling, if not eliminating, the HIV virus.
At the first conference ever devoted to the international effort to develop such a vaccine, AIDS researchers said science's understanding of HIV and the human immune system has expanded dramatically.
A mood of pessimism had dominated expectations for a vaccine in recent years. Promises for a vaccine capable of preventing infection, first aired in the early 1980s, have yet to be realised.
"I'm optimistic in a way that I wasn't just a couple of years ago," said conference organiser Mr David Baltimore, a California Institute of Technology scientist who heads the US Vaccine Research Committee.
The AIDS Vaccine 2001 conference - co-sponsored by the US government, the UN, the World Health Organization and France's Agence Nationale de Recherches sur le SIDA - comes 20 years after AIDS was first identified as a disease.
It has attracted over 1,000 scientists and community activists, including regions that have been especially hard hit by the pandemic such as Africa, which is home to 25 million AIDS or HIV sufferers.
A vaccine will provide the ultimate solution in terms of prevention, said Rwandan President Mr Paul Kagame, who called for international partnerships to make new drugs available to impoverished sub-Saharan Africa.
Twenty-two million people have died from AIDS over the past two decades, and another 36 million have become sick or been infected with the HIV virus that causes the disease.