More than three million Americans stop smoking each year, but because of the addictive nature of nicotine, most have a hard time kicking the habit for good.

Helping smokers end their addiction is the goal of an investigational vaccine against nicotine that is being studied at the UConn Health Center. NicVAX is manufactured by Nabi Biopharmaceuticals.

Here’s how it works: When a person smokes a cigarette, nicotine enters the blood and spreads throughout the body. In the brain, nicotine attaches to receptors, releasing chemicals that cause the addiction.

“Nicotine is very small and therefore the body cannot make antibodies against it on its own,” explains Dr. Cheryl Oncken, an associate professor of medicine and the principal investigator in the clinical study. “However, when nicotine is attached to a large protein that stimulates an immune response, the body is able to ‘see’ nicotine and make antibodies against it.”

According to the manufacturer, when a person is injected with NicVAX, the body makes antibodies to nicotine. With each additional shot, the body gradually makes even more antibodies.

“So when a person smokes and nicotine gets into their blood, the antibodies they now have in their blood will bind to the nicotine, making a larger molecule,” says Oncken. “This molecule is too large to enter into the brain, so it’s thought that preventing the nicotine from entering the brain may break the addiction.”

She says the goal of the vaccine is to generate antibodies to nicotine that will gradually reduce the amount of nicotine the brain sees over time, making it easier to quit smoking.

Oncken and her research team are looking for participants to take part in the nationwide study. They must be smokers between 18 and 65 years of age. They must smoke at least 10 cigarettes a day, want to quit smoking, and be in good general health.

Participants in the research study will be required to receive injections of either NicVAX or a placebo vaccine (neither the participants nor the study doctor will know who receives which injection), and also take part in counseling sessions.

All visits and the study drug (the active vaccine or the inactive placebo) are free of charge. Participants will be involved in the study for one year. After an initial screening visit, they will come to the Health Center every two to four weeks throughout the study.

For more information on this stop-smoking research program, call the smoking cessation staff at the University of Connecticut Health Center at 860-679-3136 or go to clinicaltrials.gov.