Huge excitement has greeted the news that a major late-stage trial of a combination AIDS vaccine is the first to show some effectiveness in preventing HIV.

A six-year Phase III trial involving more than 16,000 adult volunteers in Thailand has demonstrated that a vaccine combining Sanofi Pasteur's ALVAC vaccine and AIDSVAX, developed by VaxGen and now owned by the Global Solutions for Infectious Diseases, was “safe and modestly effective” in preventing HIV infection. According to the trial sponsor, the US Army Surgeon General, the prime boost combination of the two treatments lowered the rate of HIV infection by 31.2% compared with placebo.

In the analysis, 74 placebo recipients became infected with HIV compared to 51 in the vaccine regimen arm, a statistically significant result. The combo had no effect on the amount of virus in the blood of volunteers who became HIV-infected during the study, more details from which will be presented at the AIDS Vaccine Conference (October 19-22) in Paris.

Lieutenant General Eric Schoomaker, Surgeon General of the US Army, noted that this is the first HIV vaccine candidate to successfully reduce the risk of infection in humans. “We are very excited and pleased with the outcome of this trial”, he said, saying that the study, known as RV144, is “an outstanding example of international and interagency collaboration involving many partners from the Thai and U.S. governments, private companies, non-profit organisations and volunteers”.

Claiming that “this finding has important implications for the design of future HIV vaccines and how they are tested”, the sponsors acknowledged that “additional research is needed to better understand” how this vaccine regimen actually works. Nevertheless, the data has caused huge excitement and the International AIDS Vaccine Initiative’s senior vice president for R&D, Wayne Koff, said that “at the very least, these results give researchers a platform on which to improve and to validate animal models and assays, and a way to attract new investment and creative energy to the field of AIDS vaccine R&D.”

Michel DeWilde, R&D senior vice president for Sanofi Pasteur, noted that “albeit modest, the reduction of risk of HIV infection is statistically significant” and “this is the first concrete evidence, since the discovery of the virus in 1983, that a vaccine against HIV is eventually feasible”. He added that “further work is required to develop and test a vaccine suitable for licensure and worldwide use,”