Published online 24 September 2009 | Nature | doi:10.1038/news.2009.947

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Vaccine protects against HIV virus

A two-shot combo reduces the risk of HIV infection.

HIVIs an effective HIV vaccine on the horizon?Getty

The largest HIV vaccine trial to date has shown moderate success at preventing infection by the virus.

The experimental vaccine — a combination of two older shots that failed to work on their own — reduced the risk of someone contracting HIV by nearly a third. Scientists, however, are still scratching their heads as to how the double-shot approach blocks the virus.

"I don't think anybody knows why this worked the way it did," says Dan Barouch, an immunologist at the Beth Israel Deaconess Medical Center in Boston, Massachusetts. "It's the largest step forward that's ever occurred in the HIV-vaccine field, but there's a tremendous amount of more work that will need to be done."

“It's the largest step forward that's ever occurred in the HIV-vaccine field.”

Dan Barouch
Beth Israel Deaconess Medical Center

The US$119 million study involved more than 16,000 HIV-negative men and women from Thailand aged 18–30. The trial was launched in October 2003, conducted by the Thai health ministry and sponsored by the US Army Surgeon General. It tested a two-shot infection-fighting strategy using drugs made by Sanofi-Pasteur of Lyon, France, and VaxGen of Brisbane, Australia. Over the course of 24 weeks, participants received four doses of a 'primer' vaccine — a disabled bird virus containing synthetic versions of three HIV genes — and two doses of a 'booster', which consisted of a protein called gp120, a major component of HIV's outer coat. Clinicians tested for HIV infection every 6 months for 3 years.

Hybrid vigour?

Many HIV vaccine experts had previously criticized the approach as a waste of time because each of the vaccine components had a poor track record1. The primer, called ALVAC, conferred little to no immune protection in multiple early-phase clinical trials, and the booster, called AIDSVAX, had flopped twice in high-profile, large-scale trials. "I thought it was sort of a crazy trial," says David Markovitz, who studies HIV at the University of Michigan, Ann Arbor. "It was based on poor data and it didn't seem to make a lot of sense at the time."

The two-pronged vaccine did not affect the amount of virus circulating in the blood of those who acquired HIV during the study. But it did show a protective effect — vaccinated individuals were 31% less likely to become infected. New infections occurred in 74 of the 8,198 people who received dummy shots, but only 51 of the 8,197 in the vaccine group, the researchers, led by Supachai Rerks-Ngarm of the Thai Ministry of Public Health's Department of Disease Control, found. "That's not bad," says Markovitz. "It's certainly a lot better than anything else."

"The numbers of people that became infected are really small," notes Adriano Boasso, an HIV researcher at Imperial College London, UK. But the difference was statistically significant, so it's unlikely to be chalked up to chance events alone, he says.

"Up until now, we've all believed that an AIDS vaccine is possible," says Seth Berkley, president of the International AIDS Vaccine Initiative. Yet despite successes in animal models, no human vaccine — including the last big trial, known as STEP, which was halted in 2007 after the vaccine was found to increase the risk of infection — had shown any promise. So, "seeing a signal in humans is a pivotal and important part of the process of getting the product we need", Berkley says.

Boasso points out that the vaccine still has a long way to go before it gets rolled out on a larger scale. "Nobody would be considering licensing a vaccine that is 30% effective," he says. "You'd want to be aiming for 70–80% at least." Researchers should now work to optimize the vaccine or the dose schedules to improve the odds of protection, he says.

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The trial's findings will be presented next month at the AIDS Vaccine Conference in Paris, France. Until all the results are made public, Beatrice Hahn, an HIV researcher at the University of Alabama at Birmingham, cautions against getting too excited. "It looks like there's some positive effect, but I can't judge the magnitude or significance of it without seeing the details," she says. 

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  • #60150

    Finally, I don't have to live in constant fear of contracting monkey AIDs.

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