A Phase III clinical trial involving more than 16,000 adult volunteers in Thailand has demonstrated that an investigational HIV vaccine regimen was safe and modestly effective in preventing HIV infection.

According to final results released by the trial sponsor, the U.S. Army Surgeon General, the prime boost combination of ALVAC® HIV and AIDSVAX® B/E lowered the rate of HIV infection by 31.2% compared with placebo.

"This milestone is the first sign from a study in humans that it is possible to develop an effective HIV vaccine," said Larry Corey, M.D., Co-Director of the Vaccine and Infectious Disease Institute at Fred Hutchinson Cancer Research Center, and the Principal Investigator of the HIV Vaccine Trials Network (HVTN).

HVTN is an international collaboration of scientists and educators searching for an effective and safe HIV vaccine and includes Vanderbilt University's HIV Vaccine Program and the researchers who conducted the study in Thailand.

In the final analysis, 74 placebo recipients became infected with HIV compared to 51 in the vaccine regimen arm. The efficacy result is statistically significant. The vaccine regimen had no effect on the amount of virus in the blood of volunteers who became HIV-infected during the study. More detailed results of this study will be presented next month at the AIDS Vaccine Conference, Oct. 19 through 22 in Paris, France.

Kyle Rybczyk, FNP, RN, program coordinator of Vanderbilt University's HIV Vaccine Program, said the finding is important to the design of future HIV vaccines and how they are tested, however additional research is needed to better understand how this vaccine regimen reduced the risk of HIV infection.

"Every study offers more understanding, but putting it all together is the difficult task at hand," Rybczyk said. "The results won't have immediate implications for the HIV Vaccine trials at Vanderbilt. The HIV Vaccine Trials Network will look at data as it continues to be released and make decisions about the utility of the vaccines and what the future path will be for our network."

Vanderbilt is currently enrolling participants in its HVTN 505 trial which targets men who have sex with men, a group that is disproportionately affected by HIV. 

The Thai trial used two vaccines (ALVACR HIV and AIDSVAXR B/E) that were matched to the strain of HIV that is predominant in Thailand (Clade E). The study had hypothesized that the vaccine would reduce HIV acquisition by 50 percent. Corey said the study results were statistically significant, although they did not reach the level that had been specified.

"While these results are not at the level we will need to effectively control the AIDS pandemic, it is an indication that scientists will reach the goal of developing an effective HIV vaccine," Corey said. "There are several other vaccine candidates in the research pipeline and today's encouraging results will provide renewed enthusiasm for human clinical trials, as well as additional HIV vaccine discovery."