In a study, more than twice as many people given five of the shots stopped smoking than those given fewer or phony shots -- about 15 percent versus 6 percent after one year.
That is comparable to some other smoking cessation aids currently sold and could be an important new tool for people who have failed to quit on other methods, doctors said.
The results, presented Wednesday at an American Heart Association conference, encouraged some experts.
"It clearly shows promise" and merits a definitive study, said Dr. Frank Vocci, the director of medications development at the National Institute on Drug Abuse, which has given $8 million for the research so far.
The study tested NicVAX, a vaccine designed to "immunize" smokers against the rush fueling their addiction. It's made by Nabi Biopharmaceuticals of Boca Raton, Fla.
The treatment keeps nicotine from reaching the brain, taking the fun out of smoking and hopefully making it easier to give up. Some nicotine still gets in, possibly easing withdrawal, the main reason quitters relapse.