Tuesday, October 06, 2009

Thailand HIV Vaccine Trial

So about 2 weeks ago, in the New York times, there is an article discussing the results of an HIV vaccine trial in Thailand. This trial, conducted over three years by a combined group made up of the United States Army, the Thai Ministry of Public Health, Dr. Fauci’s institute, and the patent-holders in the two parts of the vaccine, Sanofi-Pasteur and Global Solutions for Infectious Diseases.

This trial, known as the RV 144 trial was performed on a group of 16,402 adult volunteers, began in 2003 and concluded in 2009. Although discussed as a phase III vaccine trial, the trial was actually a Phase IIb test-of-concept trial. It was the largest HIV vaccine trial ever conducted. The participants in the trail received a total of six immunizations over six-months: four immunizations with ALVAC-HIV and two with AIDSVAX B/E given at the same time as the last two ALVAC-HIV injections. Half of the participants received placebo vaccinations and the other half received the actual vaccinations.

The information I have found about the study does not specify the type of volunteers and this is important, because people with risky behavior such as prostitutes and IV drug users provide a much more robust test of vaccine efficacy, as these individuals are much more likely contract HIV. That said, HIV infection is relatively prevalent in Thailand due to a combination of drug abuse (HIV spreads through dirty needles and risky behavior brought on by drug-altered behaviors) and the prominent sex trade. US Army researchers have had a long-standing relationship with the Royal Thai Army, Thai Ministry of Public Health and other Thai vaccine experts, and together they developed a plan to test this candidate vaccine in Thailand.

The results from the trial, which came out two weeks ago, stating,

"Results of the trial show that the vaccine regimen is safe and 31.2 % effective at
preventing HIV infection. While this is a modest level of efficacy, it represents a major
step forward for HIV vaccines, providing the first evidence that development of a safe
and effective preventive HIV vaccine is possible."

More specifically, 74 out of 8,198 volunteers who received placebo immunizations became infected with HIV compared to 51 out of 8,197 volunteers who received a combination of two vaccines, ALVAC vCP1521 and AIDSVAX B/E. There was no difference in the viral load between the infected individuals receiving the placebo and those receiving the vaccine. Viral load is the amount of virus in an individuals blood, so if the vaccines were even partially working one would expect to see a reduction in the viral load in individuals who have received the vaccines. The fact that we do not see any difference in viral load is unexpected, although there are several reasonable explanations.

Overall, there have been a variety of opinions and a bit of skepticism at the impact of the trial. While some news outlets are trumpeting this as a major breakthrough, there are other articles, including those here and here, are less clear on the impact. The very small differences in the number of people infected make the statistics, while completely valid and accurate, less robust than one would like.

My own view agrees with this,that while the statistics show that the numbers are significant, they are still quite small and I would like to see a more robust effect ... mostly because a few people in either direction could alter the significance of the statistics. Still, I believe that the use of the prime-boost methodology and particular types of vaccines used gives us valuable information going forward, this is a small step in the right direction rather than a major breakthrough. Having said that, this is the first time that an HIV vaccine trial has shown any efficacy in terms of reducing HIV transmission, so it is wonderful to see in terms of hope that a successful vaccine is getting closer.

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