The HIV pandemic is an unprecedented global crisis but Army researchers prove there's hope in preventing the infection with this scientific advancement.

In 2003, the U.S. Army Surgeon General sponsored the world's largest HIV vaccine trial in Thailand that tested a "prime-boost" vaccine strategy comprised of two investigational vaccines, ALVAC and AIDSVAX B/E. Results of the trial show that the vaccine regime is safe and 31.2% effective at preventing HIV infection.

Coordination for the trial was lead by the U.S. Military HIV Research Program, which is centered at the Division of Retrovirology, Walter Reed Army Institute of Research, a subordinate command of the U.S. Army Medical Research and Materiel Command. The trial was conducted by the Thai Ministry of Public Health in collaboration with a team of leading Thai and U.S. researchers.

"This significant achievement was the result of longstanding relationships involving many partners from Thailand, NIAID, NIH and the DOD, among other private and commercial companies and volunteers," said Lt. Gen. Eric Schoomaker, Surgeon General, U.S. Army. "This is exciting news. Twenty-five years ago, when I was at Walter Reed [Army Medical Center], we didn't even know that HIV would become an epidemic. To think, we have come this far in our research and to be part of this trial while I was at MRMC is full circle."

The vaccine combination was based on HIV strains commonly circulated in Thailand.

"Given its modest level of efficacy, this prime boost regimen is likely unsuitable in its current form for public health purposes. Again, this vaccine was developed for HIV strains commonly circulated in Thailand. Based on the available published data, it is likely that different vaccines may be required for different regions in the world," said Col. Jerome Kim, MHRP deputy director and HIV vaccines product manager for the Army.

This successful international collaboration involved more than 16,000 Thai volunteers who were HIV-negative. Both men and women between the ages of 18 to 30 participated in the study. Half of the participants received the prime-boost vaccine regimen and half received placebo. Volunteers received vaccinations over the course of six-months and were followed for an additional three years. Volunteers also received HIV tests every six months for three years following the vaccination, and received counseling on how to prevent becoming infected with HIV.

"While these results are very encouraging, we recognize that further study is required to build upon these findings," said Col. Nelson Michael, director of the WRAIR Retrovirology Division and MHRP director.

However, the trial data establishes a new clinical benchmark to guide future vaccine development. This study may result in significant changes in the way researchers choose which vaccines to test; evaluate the immune responses to a vaccine, both in the laboratory and animal models; and design vaccine candidates.

The total cost of the trial was $105 million which was less than expected.

"The Army will continue to be an aggressive sponsor and is committed to developing a globally effective HIV vaccine to protect U.S. and allied troops from infection and to support the U.S. National Security Strategy by reducing the global impact of the disease," said Schoomaker.