by Bob Roehr
International clinical trials of what many believed to be the most promising vaccine against HIV were stopped on Sept. 21. The STEP study enrolled 3,000 participants in a joint effort by the pharmaceutical company Merck and National Institute of Allergy and Infectious Diseases (NIAID), which is part of the National Institutes of Health. It began in December 2004.
The vaccine neither reduced the number of persons who became infected nor eased the course of disease of those who became infected, according to a scheduled interim analysis. It was conducted by a data safety monitoring board, an independent panel of experts that had access to all of the data that even the trail's leaders could not see under the rules of the trial.
In fact, those who received at least one dose of the vaccine were slightly more likely to become infected with HIV than those who received a placebo. But the numbers were small – 24 of 744 and 21 of 762, respectively. Among volunteers who received two doses of the vaccine, 19 of 672 became infected, while only 11 of 691 in the placebo arm became infected.
The findings did not reach what is called "statistical significance;" the differences might possibly be explained by randomness, rather than being a product of the vaccine used.
However, what is clear is that the vaccine provided no protection, and so the STEP trial and another more recently-initiated trial were stopped. No more of the vaccine will be administered while a full and complete analysis of the data takes place. Meanwhile, study participants are being asked to continue with their follow-up visits so that they can be monitored and additional data can be gathered.
Dr. Peter S. Kim, president of Merck Research Laboratories, expressed disappointment with news of the interim analysis. "Sadly, developing an effective AIDS vaccine remains one of the most challenging tasks facing modern medicine."
NIAID director Anthony Fauci often has explained, "With other viruses, 90-plus percent (of those who become infected) can clear the virus, even smallpox and polio. The trouble with HIV is that "the natural immune response is inadequate." He said that with an HIV vaccine, researchers are trying to create what nature has not been able to.
"These data are certainly not the ones that we had hoped for," said Mitchell Warren, executive director of the AIDS Vaccine Advocacy Coalition. "However, it must be seen for what it is: The failure of a product to show efficacy in a specific trial.
"It is in no way the end of the search for an AIDS vaccine."
