THE STUDY: The world's largest test of a potential AIDS vaccine, sponsored by the U.S. Army and conducted by the Thailand Ministry of Public Health.
PARTICIPANTS: 16,402 HIV-negative Thai men and women ages 18 to 30 at average risk of infection. Half got vaccine and the rest received dummy shots.
WHAT WAS TESTED: A two-vaccine combo, ALVAC-AIDSVAX, from Sanofi Pasteur and the nonprofit Global Solutions for Infectious Diseases.
RESULTS: The vaccine lowered the risk of becoming infected with HIV by more than 31 percent – a modest benefit that scientists hope to improve.