Concern grows over failed HIV vaccine
by Matthew S. Bajko
A report that a failed HIV vaccine could increase people's risk for contracting the virus has sent shockwaves across several continents and dealt another setback to efforts aimed at combating the spread of the deadly disease.
The Washington Post reported in its October 25 edition that hundreds of volunteers in South Africa had been notified that instead of protecting them from HIV, the experimental vaccine could increase their chances of contracting it. Soon news leaked out that nearly 3,000 participants in a second study of mostly gay men in cities across the United States and six other countries had also been informed last week of the potential risk from the vaccine.
The American volunteers, including 137 San Francisco residents, had been taking part in a trial of Merck & Company's experimental HIV vaccine known as V520. AIDS researchers cut short the trial, called the STEP study, in late September after it was determined that the vaccine did not stop HIV infections.
Researchers discovered that the vaccine might have led to more infections than it prevented, reported the Post. The paper said that among those given the vaccine, 19 tested positive for HIV compared to 11 people who received a placebo.
The finding led researchers in South Africa to contact their study's 801 participants and tell the half who received the vaccine of the potential danger involved. American researchers are waiting until after a meeting in Seattle set for November 7 to determine if they should also inform all those who received the vaccine.
"There was no great shock or surprise when the study was stopped. The surprise of course, is these latest revelations," said Stephan Oxendine, a member of the trial's local community advisory board who will be attending the Seattle meeting.
Mark Feinberg, Merck's vice president for medical affairs, told the Post that unblinding the trial participants to learn who was given the vaccine could compromise continuing research from the STEP study.
"Given the complexity of the issue, we feel the best conclusions will be reached when all the data are analyzed in their entirety," Feinberg told the paper.
Until then, all trial volunteers are being told that the vaccine might lead to a possible increased risk of HIV. Anyone who took part in the trial can contact their doctor and request to be unblinded.
Dr. Susan Buchbinder, director of the San Francisco Department of Public Health's HIV Research Section, stressed that the vaccine itself did not infect people with HIV. Rather, she said it is possible that the vaccine, made from a common cold virus, weakened people's immune systems leaving them more vulnerable to HIV. Or it could be that those people in the vaccine group had riskier behaviors and were thus more at risk for becoming HIV positive.
"We still do not know if this trend [from an early look at the data] is real, or if it applies to all STEP volunteers who got this vaccine, or just certain subgroups. We also don't know if any of these effects, even if real, may be short-term, since we have relatively short follow-up from this study," said Buchbinder. "But we are committed to giving information as quickly as possible to the study volunteers who received this vaccine, because we are always committed to the safety of our volunteers, first and foremost."
Oxendine said researchers are working overtime to analyze the study data and determine what is behind the increased risk for infection.
"I don't think we know at this point," he said. "There is a lot of stuff to go through. When you have something like this come along, you have to look at all the possibilities."
The news could have a negative impact on future vaccine trials, making it that much harder to recruit participants. One South African participant given the vaccine told the Post she wouldn't have joined the study "knowing there's a risk."
In an e-mail local AIDS activist Hank Wilson wrote, "What really frightens me is that HIV vaccine research could be dealt a mortal blow. It will be almost impossible to recruit new volunteers."
Yet Buchbinder said the safety precautions put in place for the STEP study proved to be effective at catching problems early on, leading to the trial's shutdown. She hoped people would still volunteer for various studies of HIV prevention methods.
"Vaccines do not infect anyone. This was a really unexpected finding," she said. "We are being very careful about it and trying to understand what kind of effect this vaccine has."
The research section currently has nine other vaccine trials under way, and is testing a wide assortment of tools researchers hope will be effective at combating the spread of HIV.
"With 15 to 20 new infections every week in San Francisco, we need to do everything we can to find safe and effective strategies. We're working on a number of different strategies: vaccines, herpes suppression, pre-exposure prophylaxis," said Buchbinder.