AIDS vaccine fails test, is halted

Posted: April 27, 2013

WASHINGTON - The latest bad news in the hunt for an AIDS vaccine: The government halted a large U.S. study Thursday, saying the experimental shots were not preventing HIV infection.

Nor did the shots reduce the amount of the AIDS virus in the blood when people who had been vaccinated later became infected, the National Institutes of Health said.

"It's disappointing," said Anthony Fauci, head of NIH's National Institute of Allergy and Infectious Diseases. But "there was important information gained."

The study had enrolled 2,504 volunteers, mostly gay men, in 19 cities since 2009. Half received dummy shots, and half received a two-part experimental vaccine developed by the NIH. All were provided free condoms and given extensive counseling about the risks for HIV.

It is a strategy known as "prime-boost." A DNA-based vaccine made with genetically engineered HIV material is given to prime the immune system to attack the AIDS virus. Then a different vaccine, encasing the same material inside a shell made of a disabled cold virus, acts as a booster shot to strengthen that response. Neither vaccine could cause HIV.

The idea: Train immune cells known as T cells to spot and attack the very earliest HIV-infected cells in someone's body. The hope was that the vaccine could either prevent HIV infection or help those infected anyway to fight it.

A safety review this week found that slightly more study participants who had received the vaccine later became infected with HIV. It's not clear why. But the difference wasn't statistically significant, meaning it may be due to chance.

The NIH said Thursday that it was stopping vaccinations in the study but that researchers would continue to study the volunteers' health.

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