WASHINGTON, DC—An investigational HIV vaccine has been shown to be safe and moderately effective in protecting people from the virus, officials announced at the end of September.

The US Army, in conjunction with its partners, conducted testing on 16,402 HIV-negative volunteers and found that an investigational vaccine lowered the HIV infection rate by 31.2% in the 8,000 volunteers who were given the vaccine combination, compared to the 8,000 volunteers who received the placebo.

In the final analysis, 74 placebo recipients became infected with HIV compared to 51 in the vaccine regimen arm. These results prompted Army Surgeon General, Lt Gen Eric Schoomaker, to declare, “This is the first HIV vaccine candidate to successfully reduce the risk of HIV infection in humans.” The trial was designed to test the vaccine regimen’s ability to prevent HIV infection, as well as its ability to reduce the amount of HIV in the blood of those who became infected after enrolling in the trial.

More Work Ahead on Vaccine

Officials described the results showing that the vaccine regimen is safe and 31% effective at preventing HIV infections as “encouraging.” “I have a renewed sense of optimism—cautious optimism—that the possibility of improving on these encouraging results, and ultimately developing a highly effective vaccine to protect against HIV, is within our reach,” said National Institute of Allergy and Infectious Diseases Director Dr Anthony Fauci.

The vaccine trial was the largest HIV vaccine study ever conducted in humans, and tested a prime boost combination of two vaccines: ALVAC HIV Vaccine and AIDSVAX B/E vaccine. Sanofi Pasteur manufactured ALVAC-HIV, while AIDSVAX B/E was manufactured by Genentech under a license and supply agreement with VaxGen.

Officials cautioned that more research is still needed before it is determined whether the vaccine regimen will ever be licensed. They conceded that they do not yet understand how the regimen prevents HIV infection. This, and other questions regarding the vaccine candidate, could take years to answer, officials said. “We are talking about a significant amount of time. We are not talking about results from this trial being presented to the FDA for approval,” said Dr Fauci.

In addition to testing the vaccine candidate’s ability to prevent HIV infections, trial researchers also wanted to investigate whether it could reduce the amount of HIV in the blood of volunteers who became infected after enrolling in the trial. They found that it did not reduce the amount of HIV in those who became infected. Doctor Fauci said that this was one of the most important and “intriguing findings” of the trial. “This clearly begs the question of whether protective immune responses that prevent infection are related to those that control viral load. In fact, we do not know whether our current measures of the human immune response are even relevant to the protection we see in this trial,” he said.

The vaccine regimen was tested mostly in heterosexuals and more research is needed to determine whether the vaccine prevents infections in high-risk groups, such as homosexual men and intravenous drug users. In addition, the vaccine candidate was tested in Thailand and was based on the HIV strains circulating there, so it is unclear how it might work in other geographical areas.

The trial was coordinated by the US Military HIV Research Program and was carried out by the Thai Ministry of Public Health in collaboration with a team of Thai and US researchers. Study participants received the ALVAC HIV vaccine or placebo at enrollment and again after 1 month, 3 months and 6 months. The AIDSVAX B/E vaccine or placebo was given to participants at 3 and 6 months. Participants were tested for HIV infection every 6 months for 3 years. During each clinic visit, they were counseled on how to avoid becoming infected with HIV.

Trial Carried Out

Doctor Schoomaker explained that the military has had a long-standing interest in the development of an HIV vaccine for the protection of troops. “We undertook this study to achieve that important mission to protect our warriors at home and abroad,” he said. “We partner with other federal agencies—such as NIAID—whenever their responsibility to protect the public at large and ours to protect our soldiers and their families overlap. The development of an effective vaccine [directly] protects our soldiers [from infection] and indirectly protects them by reducing the burden of disease around the world.”

In the past, Army researchers in Thailand have worked with the Thai government on HIV research projects. For this particular trial, the Army coordinated with the Thai government to develop a plan to test this candidate vaccine in Thailand. “Our infectious disease experts, lab scientists, as well as those who have experience in field trials, all participated with our Thai partners and Sanofi and others to bring this trial to fruition,” said Dr Schoomaker.

NIAID and the Army funded the $105 million vaccine trial. The Thai Ministry of Health, Global Solutions for Infectious Diseases and Sanofi Pasteur provided in-kind support. The cost of the investigational vaccine trial underscores the importance of collaborations in vaccine development. According to Dr Schoomaker, “The development of a vaccine like this—$105 million dollars roughly—illustrates the burden of expense and the time required to get to an effective vaccine or effective drug today,” he said.

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