CNN Medical Producer
(CNN) - A vaccine to prevent HIV infection has shown modest results for the first time, researchers have found.
[cnn-photo-caption image= http://i2.cdn.turner.com/cnn/2009/HEALTH/09/24/hiv.vaccine/art.vaccine.gi.jpg caption="Researchers found those who received the vaccine combination were 31 percent less likely to contract HIV."]
In what is being called the world's largest HIV vaccine trial ever, researchers found that people who received a series of inoculations of a prime vaccine and booster vaccine were 31 percent less likely to get HIV, compared with those on a placebo.
"Before this study, it was thought vaccine for HIV is not possible," Col. Jerome Kim, who is the HIV vaccines product manager for the U.S. Army, told CNN.
Watch Dr. Gupta explain the study 
Kim emphasized that the level of efficacy was modest, but given the failures of previous HIV vaccine trials, "yesterday we would have thought an HIV vaccine wasn't possible."
He called the results from the trial an important first step that will help researchers work toward a more effective vaccine.