HIV Vaccine Shows "Modest" Efficacy in Phase 3 Trial

Martha Kerr

September 24, 2009

September 24, 2009 — A prime-boost HIV vaccine is safe and 31% effective in the prevention of HIV infection in the more than 16,000 adults who participated in the trial, according to the Surgeon General of the US Army, which sponsored the clinical trial of the vaccine.

"These new findings represent an important step forward in HIV vaccine research," Anthony S. Fauci, MD, director of the National Institute of Allergy and Infectious Diseases (NIAID), announced today in a National Institutes of Health (NIH) release. NIH 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," Dr. Fauci said.

The phase 3 placebo-controlled RV144 trial was launched in October 2003. It was led by principal investigator Supachai Rerks-Ngarm, MD, from the Thai Ministry of Public Health's Department of Disease Control, and was conducted in the Rayong and Chon Buri provinces of Thailand. It involved 16,402 men and women 18 to 30 years of age who had various levels of risk for HIV infection.

Investigators tested the safety and efficacy of a prime-boost regimen of 2 vaccines. The primer dose consisted of the ALVAC-HIV vaccine, a modified canarypox vaccine developed by Sanofi Pasteur in Lyon, France. The booster dose consisted of the AIDSVAX B/E vaccine, a glycoprotein 120 vaccine developed by VaxGen Inc., and now licensed to Global Solutions for Infectious Diseases, based in South San Francisco, California.

The booster vaccine is based on HIV subtypes B and E, the most common HIV strains in Thailand. Subtype B is also one of the most common strains found in the United States.

Participants received the ALVAC-HIV vaccine or placebo at enrollment and again after 1, 3, 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.

In the final analysis, 51 of 8197 participants who received the vaccine regimen became infected with HIV, compared with 74 of 8198 placebo recipients.

This level of efficacy in preventing HIV infection was found to be statistically significant, said Margaret I. Johnston, PhD, director of NIAID's Vaccine Research Program within the Division of AIDS, in the NIH release. She added that the vaccine regimen had no effect on the amount of virus in the blood of those who acquired HIV infection during the study.

"The Thai study demonstrates why the HIV vaccine field must take a balanced approach to conducting the basic research needed to discover and design new HIV vaccines and, when appropriate, testing candidate vaccines in people," Dr. Johnson said. "Both avenues provide critical information that will continue to help us better understand what is needed to develop a fully protective HIV vaccine."

More information about the Thai HIV vaccine trial is available at


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