A new vaccine tested in Thailand has protected a significant minority of subjects against HIV infection—marking the first time a vaccine has shown even partial success against the virus that causes AIDS. The 16,000-volunteer study, undertaken by the US Army, the Thai health ministry, and two drug companies, found that a combination of two vaccines cut the rate of infection by 31%. "This is a hugely exciting and, frankly, unexpected result," the head of the AIDS Vaccine Advocacy Coalition tells the New York Times.
Another surprise is that those who were vaccinated and still contracted HIV exhibited the same viral load as those given a placebo; usually a vaccine that gives partial protection at least lowers the amount of virus present. That suggests that the vaccine doesn't produce "neutralizing antibodies," but may instead help white blood cells fight the virus. The vaccine will probably not be licensed due to its low success rate, the Times notes, but the director of the study notes: "This is not the endgame. This is the beginning."