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America.gov (Washington, DC)

Africa: Successful HIV Vaccine Study Will Lead to Further Research

Merle David Kellerhals Jr.

29 September 2009

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Medical researchers in Thailand have developed an approach to prevent HIV the same way it has been treated, by using a combination vaccine to successfully halt the spread of the disease.

Public health officials announced September 24 in Bangkok that they successfully used two previously unsuccessful HIV vaccines in combination in a large, six-year study to prevent people from getting HIV, which causes AIDS. The vaccines used in the study cannot cause HIV infection because they are not made from and do not contain the whole virus, active or dead, the medical researchers said.

The combination vaccine cut the risk in 16,402 Thai volunteers by 31.2 percent, Thai Health Minister Witthaya Kaewparadai reported at a briefing. "The result of the study is a very important step for developing an AIDS vaccine. It's the first time in the world that we have found a vaccine that can prevent HIV infection," Kaewparadai told reporters.

Researchers say the results are not enough to go ahead immediately with widespread production of the combo vaccine using the "prime-boost" approach developed in Thailand. Normally, vaccine results have to exceed 50 percent before being accepted for general use, medical researchers say. Officials at the two pharmaceutical companies that manufactured the vaccines said it will take many years of testing and further research before the combo vaccine can be used widely.

STUDY BEGAN IN 2003

The study, which began in October 2003, was conducted by the Thai Ministry of Public Health with funding and support from the U.S. Army's Walter Reed Army Institute of Research and the U.S. National Institute of Allergy and Infectious Diseases (NIAID), which is part of the National Institutes of Health based in Washington. The principal investigator was Dr. Supachai Rerks-Ngarm of the Thai Ministry of Public Health's Department of Disease Control.

Thailand was selected for the $105 million study because U.S. Army medical researchers had conducted initial research when the HIV/AIDS epidemic first emerged there in the 1990s, identifying and isolating virus strains and providing the virus's genetic information to vaccine makers. The study was conducted with the full support of the Thai government because the country had an emerging problem with AIDS when the study began.

The World Health Organization (WHO) and the Joint United Nations Programme on HIV/AIDS (UNAIDS) began support work for this trial 18 years ago, in 1991, when Thailand was recommended as one of the WHO-sponsored countries in preparation for HIV vaccine trials.

A study in 2006 by the HIV Vaccine Advisory Committee found that the "trial was being conducted at the highest scientific and ethical standards and with active community participation."

The study, the largest in HIV vaccine history, was conducted in the Rayong and Chonburi provinces with 16,402 men and women ages 18 to 30 who were at various levels of risk for HIV infection, the NIAID said. These provinces were selected because the populations in both are generally stable.

"We thank the trial staff in Thailand and the United States for their years of effort in successfully conducting this study and the study participants and the people of Thailand for their long-standing support of HIV vaccine research," said NIAID Director Dr. Anthony Fauci. "These new findings represent an important step forward in HIV vaccine research."

Thai men and women were given either a placebo or the "prime-boost" combination of the vaccine ALVAC, from Sanofi Pasteur SA, which is the vaccine division of French drug maker Sanofi-Aventis; and the vaccine AIDSVAX, originally developed by VaxGen Inc. and now held by Global Solutions for Infectious Diseases, a nonprofit organization created by former VaxGen employees.

Half of the volunteers received four "priming" doses of ALVAC and two "boost" doses of AIDSVAX over a six-month period. The other half received dummy doses of a placebo. The volunteers were tested for HIV every six months for three years after the vaccinations ended.

A Public Health Ministry lab technician works with samples during an HIV vaccine study in Thailand.

NIAID said the vaccines are based on the B and E strains of HIV that commonly circulate in Thailand. Researchers readily acknowledge that they do not know why the combination works to prevent HIV infection, and that it is unlikely the combination would work in the United States, where only the B strain is most common, in Africa or elsewhere in the world.

In previous HIV vaccine trials, neither ALVAC nor AIDSVAX proved effective in preventing HIV infection when used alone, researchers said, but when used in a prime-boost approach they tend to work. The first vaccine, ALVAC, primes the body's immune system to attack HIV, and the second vaccine, AIDSVAX, strengthens the body's immune response, researchers said.

The volunteers were given thorough briefings on the potential risks associated with receiving the experimental vaccine before agreeing to participate. All were given condoms, counseling and treatment for any other sexually transmitted diseases. On each clinic visit, each volunteer was counseled on how to avoid becoming infected with HIV. Any volunteer who became infected with HIV was given free treatment with anti-retroviral therapy based on the guidelines of the Thai Ministry of Public Health.

"For the first time, an investigational HIV vaccine has demonstrated some ability to prevent HIV infection among vaccinated individuals. Additional research is needed to better understand how this vaccine regimen reduced the risk of HIV infection, but certainly this is an encouraging advance for the HIV vaccine field," Fauci said.

NIAID and its partners are working with other scientific experts to determine the next steps, including additional research of the vaccine regimen and the need to consider the impact of these new findings on other HIV vaccine candidates, NIAID said.

ADDITIONAL STUDIES NEEDED

A conference is being held in New York during the week of September 28-October 2 with dozens of researchers, vaccine makers, major research donors and HIV/AIDS groups to determine where to go next. At the conference will be medical researchers from Thailand, the U.S. Army, NIAID and independent researchers.

U.S. Army Colonel Jerome Kim, an infectious disease expert and the Army HIV vaccine product manager at the Walter Reed Army Institute of Research's Division of Retrovirology, said researchers now will try to understand why the vaccine worked in some people and how the combo vaccine blocks infections.

"Additional studies are clearly needed to better understand how this vaccine regimen reduced the risk of HIV infection," Kim said.

"The Thai study demonstrates why the HIV vaccine field must take a balanced approach to conducting both the basic research needed to discover and design new HIV vaccines and, when appropriate, testing candidate vaccines in people," said Margaret Johnston, director of NIAID's Vaccine Research Program within the Division of AIDS. "Both avenues provide critical information that will continue to help us better understand what is needed to develop a fully protective HIV vaccine."

Lieutenant General Eric Schoomaker, the Army surgeon general and commander of the U.S. Army Medical Command, said the Thai study results are important, but modest.

"I'm pleased and proud to announce the results of the trial, which for the first time ever have shown that it is possible for a vaccine to reduce the risk of HIV infection in humans," Schoomaker said September 24 in Washington. "Although the level of protection is modest, at 31 percent efficacy, the study represents a major scientific achievement."

"Military medicine is interested in research that improves global health and makes the world safer for everyone," he added.

WHO and UNAIDS said in a joint statement that the study results, representing a significant scientific advance, are the first demonstration that a vaccine can prevent HIV infection in a general adult population, and characterized the results as modestly protective.

"However, these results have instilled new hope in the HIV vaccine research field and promise that a safe and highly effective HIV vaccine may become available for populations throughout the world who are most in need of such a vaccine," the statement said.

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