Vaccine reduces risk of HIV infection by one-third in large trial

This article is more than 15 years old. Click here for more recent articles on this topic

A combination of two HIV vaccines reduced the risk of infection by almost one-third in a large trial in Thailand, the trial sponsor announced today. It is the first proof that a vaccine against HIV can protect against infection, but scientists say a lot more research will be needed before a vaccine emerges that can be given to large numbers of people.

“This is a historic day in the 26-year quest to develop an AIDS vaccine,” said Dr Alan Bernstein, executive director of the Global HIV Vaccine Enterprise.

"This is the first HIV vaccine candidate to successfully reduce the risk of HIV infection in humans. We are very excited and pleased with the outcome of this trial and congratulate all those who participated in it," said Lieutenant General Eric Schoomaker, Surgeon General, U.S. Army, the trial sponsor.



A pill or liquid which looks and tastes exactly like a real drug, but contains no active substance.


A patient’s agreement to take a test or a treatment. In medical ethics, an adult who has mental capacity always has the right to refuse. 

statistical significance

Statistical tests are used to judge whether the results of a study could be due to chance and would not be confirmed if the study was repeated. If result is probably not due to chance, the results are ‘statistically significant’. 


The result of a statistical test which tells us whether the results of a study are likely to be due to chance and would not be confirmed if the study was repeated. All p-values are between 0 and 1; the most reliable studies have p-values very close to 0. A p-value of 0.001 means that there is a 1 in 1000 probability that the results are due to chance and do not reflect a real difference. A p-value of 0.05 means there is a 1 in 20 probability that the results are due to chance. When a p-value is 0.05 or below, the result is considered to be ‘statistically significant’. Confidence intervals give similar information to p-values but are easier to interpret. 

informed consent

A patient’s agreement to continue with a clinical trial, a treatment or a diagnostic test after having received a full written or verbal explanation of the risks, benefits and the possible alternatives. 

The trial, called RV 144, compared a regimen of vaccination with two products against vaccinations with a dummy, inactive substance in 16,000 adults enrolled since 2003.

The study recruited adults in the community in two provinces of Thailand with high HIV prevalence (Chon Buri and Rayong), but did not specifically target individuals at high risk of HIV infection. Volunteers for the study were adults aged 18-30 who gave informed consent to participate in the trial.

Participants were randomly assigned to receive an initial set of vaccinations with ALVAC, and follow-up booster vaccinations with AIDSVAX, a product previously tested in large trials without evidence of success, or the placebo vaccination.

The presence of AIDSVAX in the vaccination regimen was one reason why many vaccine experts had not expected the trial to show a positive result.

In the event, the prime-boost combination of ALVAC(R) HIV and AIDSVAX(R) B/E lowered the rate of HIV infection by 31.2% compared with placebo. This reduction was statistically significant, meaning that the possibility that the possibility of the result being due to chance is very low, but the confidence intervals for the estimate in the reduction in risk were wide (p=0.039, 95% confidence interval 1.1% - 51.1%).

In the final analysis, 74 placebo recipients became infected with HIV compared to 51 in the vaccine regimen arm. The vaccine regimen had no effect on the amount of virus in the blood of volunteers who became HIV-infected during the study.

More detailed results of this study will be presented next month at the AIDS Vaccine Conference, October 19 - 22 in Paris, France.

The vaccine products used in the study will not go forward for immediate licensing. Instead, the results from the study, which was considered to be a `proof of concept` trial, will be used to inform the design of future vaccine trials.

Collaborating partners on this study include the U.S. Army, the Thai Ministry of Public Health, the United States National Institute of Allergy and Infectious Diseases, part of the National Institutes of Health, sanofi pasteur (the developer of ALVAC), and Global Solutions for Infectious Diseases (GSID), the current developer of AIDSVAX. The collaborators are already working with external experts to determine the need for additional studies on this vaccine regimen and consider the impact of this study’s findings on other HIV vaccine candidates.

More information and analysis

See also An unpopular vaccine study produces surprising result.

See also Vaccine trial "is the beginning" of a new path of research, says US health chief.

Further information

See's guide to The search for an HIV vaccine for further background information.

Note to editors

We are happy for you to link to this article on