BANGKOK (AP) -- The world's largest AIDS vaccine trial is being hailed as a watershed event because it's the first time an experimental vaccine has prevented infection with the virus.
The result also surprised scientists because recent failures led many to think such a vaccine might never be possible.
Researchers in Bangkok announced the vaccine cut the risk of becoming infected with HIV by more than 31 percent.
Col. Jerome Kim, who helped lead the study for the U.S. Army, says the benefit is modest but is "the first evidence that we could have a safe and effective preventive vaccine."
The National Institute of Allergy and Infectious Diseases co-sponsored the study and its director, Dr. Anthony Fauci, warned that it's "not the end of the road." But he says he is surprised and very pleased.