In September the AIDS community took a devastating blow when Merck halted an international human trial of the world's most promising potential vaccine against HIV. At the time, doctors revealed only that the vaccine—which uses an "adenovirus," or the common cold virus, to deliver HIV genes into the body—had not worked.
On Wednesday they began to explain why, releasing the first data from the trial, which was run by Merck, the HIV Vaccine Trial Network and the National Institute of Allergy and Infectious Diseases. The researchers announced a troubling finding: the number of HIV infections among the trial volunteers who received the vaccine was higher than the rate among those who received a placebo. Twenty-four of 741 volunteers who got the vaccine became infected with HIV, as did 21 in the placebo group.