A follow-up study on an AIDS vaccine trial that had to be stopped early has confirmed the worst fears of researchers: The vaccine made it more likely, not less, that some men would become infected with H.I.V.
Men who were not circumcised and who had previously caught common colds caused by the same virus used to make the vaccine were two to four times as likely as other men to become infected if they got the vaccine, the study concluded.
The new study shed no new light on how that happened. "I really wish I could tell you why, but I can't," said Dr. Ann Duerr, a vaccine specialist at the Fred Hutchinson Cancer Research Center in Seattle, who led the data analysis for the new study.
The trial of the Merck vaccine, which involved 3,000 volunteers in nine countries, began in 2004 and was abruptly halted in late 2007 when it became clear that it was not protecting anyone and suspicions arose that it was making some men more susceptible.
It was a frustrating failure and had repercussions across the AIDS vaccine field. Nine months later, government investigators canceled a trial of a similar vaccine because they were not sure why Merck's had failed.
The search for an AIDS vaccine has proceeded slowly and cautiously since then. The only success in the field — and there are many skeptics who doubt even the weak success that was proclaimed — came in 2009. A vaccine called RV 144 that was tested on 16,000 Thai volunteers seemed to lower, at least temporarily, a man's chances of getting infected with H.I.V. by about 31 percent. But why that one worked, albeit badly, has remained a mystery.
The new study was published online in The Journal of Infectious Disease.
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