Thailand HIV vaccine trial first to show preventive effect

25 September 2009

The world's largest clinical trial of an investigational vaccine regimen has been shown to be well-tolerated and to have a modest effect in preventing HIV infection.

The trial, which was started in 2003 and conducted on over 16,000 men and women in Thailand, found the vaccine regimen to be safe and 31% effective in preventing HIV infection. It did not, however, reduce the amount of virus in the blood of those who became infected during the study.

The clinical trial was led by principal investigator Supachai Rerks-Ngarm, MD, of the Thai Ministry of Public Health’s Department of Disease Control. The study was sponsored by the US Army in collaboration with the US National Institute of Allergy and Infectious diseases (NIAID), pharmaceutical company Sanofi Pasteur and non-profit health organization GSID.

“These new findings represent an important step forward in HIV vaccine research,” says Anthony S. Fauci, MD, director of the National Institute of Allergy and Infectious Diseases (NIAID), part of the NIH, which provided major funding and other support for the study. “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.

The Thai Phase III HIV vaccine study, also known as RV144, opened in October 2003. The placebo-controlled trial tested the safety and effectiveness of a prime-boost regimen of two vaccines: ALVAC-HIV vaccine (the primer dose), a modified canarypox vaccine developed by Sanofi Pasteur, based in Lyon, France; and AIDSVAX B/E vaccine (the booster dose), a glycoprotein 120 vaccine developed by Vaxgen Inc., and now licensed to Global Solutions for Infectious Diseases (GSID), based in South San Francisco, Calif.

The vaccines are based on the subtype B and E HIV strains that commonly circulate in Thailand. The subtype B HIV strain is the one most commonly found in the United States.

The trial, conducted in the Rayong and Chon Buri provinces in Southeast Thailand, enrolled 16,402 men and women ages 18 to 30 years old at various levels of risk for HIV infection. 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 counselled on how to avoid becoming infected with HIV.

In the final analysis, 74 of 8,198 placebo recipients became infected with HIV compared with 51 of 8,197 participants who received the vaccine regimen. This level of effectiveness in preventing HIV infection was found to be statistically significant. The vaccine regimen had no effect, however, on the amount of virus in the blood of volunteers who acquired HIV infection during the study.

“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,” says Margaret I Johnston, PhD, 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.”

Donald Francis, MD, DSc, GSID’s Executive Director said, “As the first HIV vaccine trial to demonstrate some level of reduced infection among the entire trial population, this is an encouraging step forward in the struggle to develop an effective HIV/AIDS vaccine. This trial will provide researchers with valuable data and insights to continue the development of a vaccine that can hopefully one day eradicate this terrible disease.”

NIAID and the collaborating partners are working with other scientific experts to determine next steps, including additional research of the RV144 vaccine regimen and the need to consider the impact of these new findings on other HIV vaccine candidates.

Additional research will be required to clarify the public health benefits of this outcome, including whether boosters would be needed and whether the vaccine combination would yield the same results against different strains of the virus found in other parts of the world. One of the most critical steps now would be to manufacture new lots of
AIDSVAX for a variety of possible future studies in combination with ALVAC. GSID would make AIDSVAX at a qualified contract manufacturer.

Individuals who acquired HIV infection while participating in the Thai trial have been provided access to HIV care and treatment, including highly active antiretroviral therapy based on the guidelines of the Thai Ministry of Public Health.

More information

The Thai Phase III HIV vaccine trial, please see the US Military HIV Research Program: 


See also:

Revolutionary antibody technology gives hope for vaccine against genetically diverse HIV

HIV vaccine a step closer with discovery of new potent antibodies

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