The results of the study were published in the New England Journal of Medicine and presented at the annual AIDS Vaccine 2009 conference in Paris on 20 October, 2009.

 

The trial was the largest of its kind, with over 16 000 people in Thailand participating. When the initial results were released the study found that the vaccine had prevented new infections in HIV-negative people.

 

Known as the Thai Phase III HIV vaccine study, the trial was conducted on people aged between 18 and 30 by the Thai Ministry of Health and was sponsored by the US Army and the National Institute of Allergy and Infectious Diseases.

 

It used a combination of two vaccines that were previously tested separately with no success.  

 

The combination, known as RV-144, was designed to smuggle fragments of HIV into the body, prompting the body to produce t-cells to kill the virus and prevent the virus from infecting new cells and replicating in the body.

 

During the trial 8 197 people were given the vaccine and 8 198 were given the placebo. All volunteers were given condoms and information on how to prevent transmission of HIV.

 

After the six-year trial, the reported results were that those who had received the vaccine were 31% less likely to become infected than those who had not received the vaccine. However, the scientific community has criticised the way this conclusion was drawn.

 

According to an article on the AIDS Beacon titled Guide to the Thai HIV Vaccine Trial Results – What do they mean? Why are they in question?, “The questions about the study revolve around the issue of statistical significance. Statistical significance is calculated in order to confirm that a study’s results are meaningful and not due to chance.”

 

At the end of the study participants were put into three categories to determine the statistical significance of the results.

 

The Intent-to-Treat (ITT) group contained all 16 395 participants, including those people who were later found to be unsuitable. The ITT group included seven volunteers who were HIV-positive when the trial started.

 

The second group was the Modified Intent-to-Treat (mITT) group and excluded the seven subjects who were later found to be ineligible for the study and the people who did not receive all six injections of the HIV vaccine.

 

The third group was called the Per-Protocol (PP) group and included only the participants who completed the trial and received the full treatment or dosage.  

 

In the RV-144 study the results from the mITT group were the only results that met the accepted scientific standards of statistical significance. And if researchers look at this group only, they cannot rule out the possibility that the results were due to chance and not from the protection of the vaccine.

 

The way that the data from the trial was analysed has been heavily criticised, but Colonel Nelson Michael, the primary investigator of the US Military HIV research team, says that the media and other researchers misunderstood the reason for the study.

 

He suggested the trial was meant to test a “proof of concept”, to discover whether a combination of two vaccines would have a preventative effect at all.

 

The way that the results were released has also been criticised as the researchers did not give any indication that the results that they presented were only from the mITT group.

 

In a press release, Michael Weinstein, president of AIDS Healthcare Foundation (AHF), said: “Following the repeated failures in AIDS vaccine research over the years, the premature and partial reporting of select – and favourable – vaccine trial data here underscores an inherent and glaring conflict of interest.”

 

Within the research community there have been calls for the results to be independently assessed by a group of external researchers.

 

But there are researchers who maintain that, although the results are not as promising as originally thought, there is potential for this research to inform further work.

 

Deborah Jack, chief executive of the National AIDS Trust in the United Kingdom, called the Thai trial “a milestone in the search for a vaccine against HIV.”

 

She said: “These results are an incredible opportunity for scientists to discover new clues about HIV and learn how an HIV vaccine could work in practice."