Madison (Wisconsin), July 28 (AP): Doctors are testing a radical new way to help smokers quit: a shot that “immunises” them against the nicotine rush that fuels their addiction.

That pleasurable buzz has seduced Mario Musachia into burning through nearly half a million cigarettes in half a century. Now the Madison man is among 300 people around the country who are testing an experimental vaccine that makes the immune system attack nicotine in much the same way it would fight a life-threatening germ.

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.

After four smaller studies suggested that the vaccine might be safe and effective, the new, larger study was started in Madison, Minneapolis, Omaha, San Francisco, Los Angeles, and New York.

The Food and Drug Administration has granted the vaccine fast-track status, meaning, it will get prompt review.

“It’s going to be a very good way to keep people from relapsing,” predicts Dr Frank Vocci, director of medications development at the federal institute.

Relapse is the biggest problem quitters face. Of the more than 48 million smokers in the US, 40 per cent each year make a serious attempt to quit, but fewer than 5 per cent succeed long-term. Nicotine replacement products combined with counselling can double that rate, but most quitters do not try them. Two-thirds go back to smoking within a month.

The possibility that a simple shot could do this is what lured Musachia to the Center for Tobacco Research and Intervention on the fringes of the University of Wisconsin-Madison campus earlier this month. He has tried many ways to quit but still smokes.

“I’m sick of it. I’m surprised I’ve lived this long,” said the 75-year-old man. “My kids ' they carry on like 2-year-olds when I smoke around them. My animals run and hide.”

He and other participants will get four or five shots, either four or six weeks apart, and will be studied for a year. Two-thirds will get the vaccine; the others, dummy shots. Neither they nor the doctors will know who got what until the study ends.

They also will get counselling and must set a quit date, usually around the second shot, because the first shot is just meant to “prime” the immune system.