A vaccine is not exactly a novel invention, but one that's designed to fight HIV certainly is. More than 20 years after the AIDS virus was identified, researchers have devised the first immunization to protect people against HIV infection. A six-year trial showed that the vaccine, which consists of two shots that given individually had failed to protect against HIV, is modestly effective, reducing infection 31% among those receiving the regimen vs. those getting a placebo. Scientists are still trying to figure out how the vaccine decreases infection risk, since the shots did not affect the level of virus in the blood of volunteers. And some experts question whether the small effect is indeed significant. The vaccine is not approved for use yet, but it's the first to make any headway against HIV, and that's a start.