An effective Aids vaccine is still at least a decade away, according to experts attending a conference this week in the Swiss city of Lausanne to assess the latest research.
Giuseppe Pantaleo, conference chairman and professor at Lausanne university hospital, said a vaccine was unlikely before 2014 ?and perhaps even later?.
He and others urged a greater European commitment to vaccine research, now overwhelmingly concentrated in the US.
Seth Berkley, head of the international Aids vaccine initiative (Iavi), called for a doubling of resources to $1.1bn (?904m, ?614m) a year and new collaborative initiatives between the public and private sectors to accelerate vaccine development.
?Every year we wait, millions will be infected and condemned to death?, Dr Berkley said on Thursday in Geneva. ?Only a vaccine can end the epidemic.?
About 5m people a year are newly infected with HIV (human immunodeficiency virus), which causes Aids (acquired immune deficiency syndrome), and 3m a year now die from the disease.
Wayne Koff, Iavi's chief of vaccine research, said developing an effective Aids vaccine was ?the hardest challenge we've ever faced in terms of a vaccine?.
More than 30 candidate vaccines against HIV are being tested in human clinical trials in 19 countries, the majority begun in the last four years.
Only one candidate vaccine, VaxGen's AIDSVAX, has gone through large-scale trials, the results of which were disappointing.
Dr Koff said a fully protective vaccine would need to stimulate HIV antibodies as well as kill infected cells, the focus of almost all the current candidate vaccines.
Killing infected cells, by keeping viral loads at low levels, could delay development of full-blown Aids in HIV-positive people from an average of 10 to perhaps 20 years, but would not prevent HIV infection.
Researchers are still at an early stage in looking at vaccines that could elicit HIV antibodies. In the meantime, Iavi is pressing for all the existing candidate vaccines to undergo the necessary clinical testing.