Quitting smoking is tough - so tough that only about 5 percent of smokers who try to quit in a given year actually succeed. Medications can double those odds - which still leaves a high failure rate. And a promising vaccine, meant to arouse an immune response to nicotine, could not beat a placebo in clinical trials. But researchers haven't given up on a vaccine just yet. Instead of revving up the immune system, though, they've come up with a new idea: why not use an enzyme to break down nicotine - before it gives you a buzz?