The National Institute of Allergy and Infectious Diseases (NIAID), part of the National Institutes of Health (NIH), supports HIV/AIDS research and development. In the past few weeks, several decisions will substantially contribute to a federal effort to develop preventive HIV vaccines in the future.

NIAID states they have a common goal: "to prevent the further spread of HIV/AIDS by developing safe and effective vaccines, other prevention strategies and innovative HIV treatments." One of the more promising vaccine development programs that is being led out of the NIAID is the HIV Vaccine Trials Network (HVTN). HVTN was established by NIAID in 1999 to foster the development of HIV vaccines through testing and evaluating candidate vaccines in clinical trials. The network spans four continents and has the capacity to conduct all phases of clinical trials, from evaluating candidate vaccines for safety and the ability to stimulate immune responses, to testing vaccine efficacy.

Until recently, NIAID and the U.S. Army had proposals under way to begin large-scale, Phase III HIV vaccine efficacy trials in the near future. Both trials were to test similar "prime-boost" vaccine combinations (a canarypox virus-based primer vaccine followed by a "gp120" subunit booster vaccine). The canarypox vaccine combinations that the NIAID and U.S. Army were going to use were slightly different and answer different important scientific questions surrounding HIV vaccines. The main difference between these trials was that the U.S. Army trial was going to be tested mainly in Thailand and the NIAID trial was going to be tested primarily in the United States.

However, NIAID has decided not to proceed with a three-arm Phase III HIV vaccine efficacy trial, (also known as HVTN 501). That decision, made by NIAID and HVTN leadership, in consultation with other vaccine developers and the manufacturers of the vaccine candidates, was based on recently learned preliminary immunogenicity results of a Phase II trial (HVTN 203) of its canarypox prime-boost candidates.

The decision not to proceed with HVTN 501 does not mean the vaccine products are not efficacious. Several different immune tests are being developed and tested with the vaccine product to help determine which immune test and vaccine candidate will correlate with HIV protection in humans. For this reason, the Thailand study will continue. Aventis Pasteur and VaxGen have made efforts in the development of an HIV vaccine and they will continue to have involvement in the Thailand trial to assess the efficacy of their prime-boost vaccine.

NIAID will continue to support research and development to advance vaccine products. In the next few years, further studies and discussions with stakeholders at domestic and international sites will help guide decisions regarding the future development and testing of canarypox HIV vaccine candidates.

In the future, HVTN's network experience in conducting international vaccine development and testing and its collaborative ties in many parts of the world will enhance global efforts to develop an effective AIDS vaccine.

For more information on NIAID, please contact: www.niaid.nih.gov/daids/vaccine/default.htm.

For more information on the HIV Vaccine Trials Network (HVTN) and their current vaccine efforts, please contact: www.hvtn.org.