"The AIDS virus infects 33.4 million people globally, according to the United Nations agency UNAIDS. It has killed more than 25 million people. Because it is spread in so many ways -- during sex, on needles shared by drug users, in breast milk and in blood -- there is no single easy way to prevent infection. A vaccine is the best hope."

Reuters reports:

AIDS experts and advocates gathering in Vienna this weekend for a conference on the pandemic will hear about progress in protecting people from the deadly virus using drugs, and ways to affect behavior.

No breakthrough news is expected on a vaccine. But researchers are more hopeful than they have been in years that it may be possible. They just have to choose the best path to pursue.

Two studies published in the past year have greatly raised hopes. In one published last September, a combination of two older vaccines lowered the infection rate by about a third after three years among 16,000 ordinary Thai volunteers.

In a second study, published earlier this month, researchers discovered human antibodies that can protect against a wide range of AIDS viruses. They found the antibodies in the blood of some people whose bodies made them after they were infected with HIV. Two of them attached to and neutralized 90 percent of the various mutations of HIV.

But the road is littered with the remains of failed vaccine attempts.

In 2007, Merck & Co ended a trial of its vaccine after it was found not to work, and in 2003, AIDSVAX used alone was found to offer no protection, either. READ MORE