Major news out of Thailand—for the first time ever, an experimental vaccine has cut the risk of contracting HIV by more than 31 percent, a modest benefit, but the first evidence that a preventative vaccine could be possible. The trials, run by the Thailand Ministry of Public Health, involved more than 16,000 volunteers in Thailand and used a two-vaccine combo in a "prime boost" approach, where the first shot primes the immune system to attack HIV and the second shot boosts immune response. The study followed HIV-negative Thai men and women at an average risk for infection over three years. All study participants received condoms, treatment for sexually transmitted diseases, counseling, and free treatment for HIV. Over three years, 51 people of the 8,197 given the vaccine developed HIV, compared with 74 of the 8,198 in the control group. It's unknown whether the vaccine would work against HIV strains in the U.S., Africa, or elsewhere.