Of the nearly 34 million people in this country who have tried to quit smoking, only 1.2 million have actually managed to kick the habit permanently, according to the United States Centers for Disease Control and Prevention. But a new vaccine, called NicVAX, could make it easier for quitters to win. NicVAX works by preventing nicotine from entering the brain where it normally acts as a stimulant. "An immunized tobacco user would theoretically receive no positive reinforcement from nicotine use," said Robert Naso, Ph.D., a senior vice president at Nabi Biopharmaceuticals, which developed the vaccine. Final approval for NicVAX could take several years.