If previous trials of AIDS vaccines hadn’t been so disappointing, the results out today from the latest trial wouldn’t seem so promising. Put another way: The results aren’t particularly strong, as far as vaccines go — the vaccine combination used in the study won’t be able to stop the spread of HIV around the globe. But, given the history of AIDS vaccine failures, any benefit at all is something worth noting. Over the course of three years, 74 of 8,198 people who received placebo shots became infected with HIV, compared with 51 of 8,197 people who received vaccine. So the vaccine appeared to reduce the risk of being infected by 31%. The statement from NIH , one of the sponsors of the trial, called this a “modest preventive effect.” Patients who received the vaccine and did get infected didn’t have lower levels of virus than patients who received placebo and got infected — a puzzling finding, given that a partially effective vaccine would be expected to help a patient’s immune system fight

the disease. Still, previous AIDS vaccine trials have failed miserably. A Merck AIDS vaccine study was halted in 2007, after data showed the vaccine didn’t reduce the risk of infection and may actually have left some people more susceptible to the virus. The NIH subsequently canceled plans for another major AIDS vaccine trial that would have used a similar approach. Anthony Fauci, who heads the infectious diseases unit at NIH, told the AP that the results of the latest trial give him “cautious optimism” but also said the findings are “not the end of the road.” The study, known as RV144, was conducted in Thailand and used a combination of two vaccines. For more information, check out this page from the U.S. military’s HIV research program, another sponsor of the study. And Clinicaltrials.gov has an overview of the study basics, and a complete list of sponsors and collaborators. Image of HIV by C. Goldsmith via CDC

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AIDS Vaccine Trial: Why a ‘Modest’ Benefit Is Notable