The fight against AIDS has reached a "watershed," said Marilynn Marchione and Michael Casey in the San Francisco Examiner. Researchers announced in Bangkok Thursday that an experimental vaccine had cut the risk of infection with HIV—the virus that causes AIDS—by 31 percent in a trial of more than 16,000 volunteers. This was the largest AIDS vaccine trial yet, and the first time a drug had prevented infection with the AIDS virus.

There's no question this is significant, said Donald G. McNeil Jr. in The New York Times, but this new HIV vaccine still "protected too few people to be declared an unqualified success." And it left scientists "delighted but puzzled"—the RV 144 vaccine was actually a combination of two genetically engineered vaccines, but neither of them had worked before in humans.

Sure, there are plenty of questions raised by this trial, said Scott Hensley in, but it "gave new hope to scientists that, in principle, a vaccine could work someday." The success of this AIDS vaccine was "modest," but every other experimental vaccine has failed outright. This was a step toward a drug that really works to prevent the spread of the HIV virus —and that would be the "ultimate weapon" in the fight against AIDS.