New Jersey ? New data on an experimental AIDS vaccine that failed to work shows volunteers who got the shots were far more likely to get infected with the virus through sex or other risky behavior than those who got dummy shots.

The new details, released Wednesday by drugmaker Merck & Co., don’t answer the crucial question of whether failure of the vaccine also spells doom for many similar AIDS vaccines now in testing.

And researchers weren’t sure why more of the vaccinated volunteers wound up getting HIV than those who got dummy shots.

Merck, based in Whitehouse Station, N.J., announced on Sept. 21 that it was stopping the study because the vaccine didn’t work. It was a stunning setback in the push to develop an AIDS vaccine.

The vaccine is made from a common cold virus with three synthetic HIV genes tucked inside. It’s designed to stimulate the immune system to kill any HIV-infected cells encountered in the future.

However, the researchers found that volunteers with pre-existing immunity to this particular cold virus were much more likely to get infected with HIV if they got the AIDS vaccine than if they got the dummy shot.