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NicVax targets nicotine, a tobacco chemical that, once in the brain, induces addiction to cigarettes.

"Based on the animal model data that we've got, this vaccine is very effective in really blocking the effects of nicotine," Nabi Senior Vice President Robert Naso said.

The vaccine triggers the immune system to build antibodies that attach to nicotine molecules. That makes them too large to enter the brain, so the body just wastes them away instead.

"And if we can block nicotine from getting into the brain," Naso said, "we can block the effects of nicotine in the body."

That strategy might help smokers such as Michael Cole, who's gone through a pack a day for the last 17 years.

"I tried to quit about three or four times," Cole said. "I plan on trying it again."

Cole is like two of every three smokers who try to quit but end up smoking again. Their habit contributes to a $100 billion a year medical bill that's linked to cigarette smoking. If nicotine keeps Cole coming back for more, the vaccine might help him lose interest.

Researchers say they feel NicVax provides an added dimension to classes and programs that help smokers quit. But skeptics wonder what happens if smokers just smoke more cigarettes — inhaling more nicotine than the vaccine can handle — and remain addicted anyway.

"In theory, if you took in enough nicotine, you could overcome the effects of the antibody and you would still get the nicotine effect," said Dr. Neil Benowitz, a nicotine researcher at the University of California in San Francisco.

That's one of the issues being explored through clinical trials. This first trial, though, involves nonsmokers and will only assess whether the drug is safe. If future trials prove that NicVax works, the manufacturer expects to win clearance for its drug within five years.