At the end of February, thousands of the world’s leading HIV researchers and a few advocates met at the 14th Conference on Retroviruses and Opportunistic Infections (CROI). CROI, as it is known, is a scientific conference for HIV researchers in both the treatment and prevention areas.

Merlin Robb presented on the number of HIV vaccine efficacy trials planned or in the works. These trials are looking at the ability of a vaccine candidate to prevent infection or to slow or stop progression to AIDS. One trial, by the U.S. Military HIV Research Program, is testing a canary pox HIV vaccine with a protein boost in a large-scale clinical trial with 16,000 volunteers in Thailand. Another Merck-sponsored adenovirus vector candidate is being tested in 3,000 volunteers in the U.S. and Latin America. The adenovirus vaccine is based on a form of cold virus made harmless.

Two additional efficacy trials are also planned. A South African trial of the Merck candidate is scheduled to start this year, and a trial of the Vaccine Research Center (VRC) adenovirus vaccine is also planned. The canary pox vector vaccine is expected to have results by June 2009, with results from the Merck U.S. and Latin America trial by 2010. The South African trial of the Merck candidate is expected by June 2011, and the results of the VRC trial are expected about the same time.

Researchers believe that the Merck and VRC adenovirus vaccines have strong immunologic responses shown by higher levels of T-cells that recognize HIV. These T-cells could be stimulated to attack HIV infected cells and to slow HIV replication. Dan Barouch presented on a second generation of adenovirus vaccines that may provide even higher immune responses. The vaccines in efficacy trials will not generate the neutralizing antibodies thought by some necessary to prevent infection. Dennis Burton of Scripps presented a talk on why antibodies are so difficult to generate and suggested that an effective vaccine may need both antibody and T-cell responses.

Over the next few years we will begin to hear the results of clinical trials of these vaccine candidates. If they succeed, additional clinical trials may be necessary before they can be licensed. If these vaccines slow disease rather than prevent it, the vaccine field will also need to think about how they can be introduced and how they fit into the entire spectrum of HIV prevention technologies.

Kevin Fisher is the Senior Policy and Strategy Advisor for the AIDS Vaccine Advocacy Coalition (AVAC) in New York City. He can be reached atkevin@avac.org.