The treatment keeps nicotine from reaching the brain, making smoking less pleasurable and theoretically, easier to give up. The small amount that still manages to get in helps to ease withdrawal, the main reason most quitters relapse.
If it works _ and this has not yet been proved _ the vaccine could become part of a new generation of smoking cessation treatments. They attack dependency in the brain instead of just replacing the nicotine from cigarettes in a less harmful way, like the gum, lozenges, patches and nasal sprays sold today.