An AIDS vaccine candidate previously reported to have partial efficacy may have been most useful during a short timeframe, researchers announced Thursday at the 17th Conference on Retroviruses and Opportunistic Infections in San Francisco. The vaccine's temporary protection may have waned after a year or so, making it more difficult to assess its effects, reported Dr. Nelson Michael, of the Walter Reed Army Institute of Research, and colleagues.

"It is very likely that this vaccine only worked for a short period of time," Michael said. The trial in Thailand showed a 31 percent cut in infection risk over a longer timeframe of three years. "It is a weak, a modest effect but something that we can build on." The vaccine is a combination of Sanofi-Pasteur's ALVAC canarypox/HIV vaccine and AIDSVAX, made by VaxGen and now owned by the nonprofit Global Solutions for Infectious Diseases.

Though the trial enrolled 16,000 volunteers, they were not individuals at particularly high risk of HIV infection, Michael said. Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, and Michael will work together to design a trial in Asia or Africa to better determine whether the vaccine can be useful.

"Is [short-term protection] ideal? No," said Michael. "But it is true there are vaccines like the flu vaccine where you have to get them every year." Researchers next will examine the blood of trial participants to look for clues as to why the vaccine worked. Labs around the world will be searching for correlates of efficacy, such as measurements of antibodies that indicate some immune system response, Michael said. Those results could take roughly a year.

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