AIDS vaccines experts confused and dismayed

By Maggie Fox, Health and Science Editor - Analysis

WASHINGTON (Reuters) - AIDS vaccine researchers are worried about the future of their field after learning an experimental HIV vaccine not only does not work, but just might make recipients more susceptible to infection with the AIDS virus.

They are worried about their volunteers and the future of AIDS vaccines in general. And they are worried because they cannot understand how a vaccine would make a person more vulnerable.

Researchers from Merck & Co. (MRK.N: Quote, Profile, Research), which makes the vaccine, and the National Institute of Allergy and Infectious Diseases, which is helping develop it, said on Wednesday they believe a type of common cold virus used as the basis of the vaccine may somehow have made their volunteers more susceptible to HIV.

They are meeting this week in Seattle to hash through the data and figure out what happened.

This is what they know: Out of 1,500 people vaccinated, 82 became infected with the AIDS virus. Of these, 49 got the vaccine and 33 got a placebo shot.

While they are counseling volunteers that they may have raised their own risk of becoming infected, they are also trying to figure out what happened.

"The data are disappointing and puzzling but we don't have definitive answers," Dr. Lawrence Corey of Fred Hutchinson Cancer Research Center in Seattle, who was organizing the trial, told reporters.

Only one woman in the trial became infected with HIV. The rest were men having sex with other men, and it was the men who started out with the highest immune response to the adenovirus 5 common cold bug used to make the vaccine who were the most likely to become infected with the AIDS virus.