Chicago ? Vaccines, the most potent medical weapon ever devised to vanquish deadly germs, now are being called on to do something totally different and culturally revolutionary – inoculate people against bad habits like overeating, cigarette smoking and drug use.

Whether this new era of vaccine research actually can subdue many of the poor lifestyle choices that are today’s biggest threats to health – causing obesity, cancer, heart disease and other problems – has yet to be proved.

But the evidence is promising enough to persuade the federal government to put millions of dollars toward finding out if two of the vaccines can end nicotine and cocaine addiction.

The National Institute on Drug Abuse, which has spent $15 million on clinical trials for the vaccines and plans to spend more, predicts that one of the nicotine vaccines may be available for marketing in three years.

“The American Cancer Society has projected that we will have 1 billion people die from smoking in the world in this century,” said Frank Vocci, director of medications development for the institute. “If you had a vaccine that helped people quit and stay quit, or prevent them from smoking, that’s where you’d get the greatest public health benefit.”

Meanwhile, results from a major obesity vaccine trial under way in Switzerland are expected later this year, and company officials are hopeful the vaccine could be ready for use in a few years if all goes well.

To tamp out deleterious behavior, the new vaccines employ the body’s natural immune system in an innovative way. Instead of building antibodies to destroy germs as traditional vaccines do, they construct antibodies that lock onto nicotine and cocaine molecules, preventing them from reaching the brain.

“What we’re seeing is a renaissance in vaccine technology,” said Dr. Gary Nabel, director of the National Institute of Allergy and Infectious Diseases’ Vaccine Research Center. “It’s only natural that when you have a technology that’s this powerful it can be applied to other medical problems.”

Normally, nicotine and cocaine molecules are too small to be seen by the immune system. So to make the vaccines, scientists attach these molecules to big target proteins, like harmless viruses or bacteria, which the immune system can recognize and attack with specialized antibodies.

When the person later smokes a cigarette or takes cocaine, the antibodies wrap up and neutralize the molecules before they can trigger feelings of euphoria and pleasure in the brain. Smokers and cocaine users given the vaccines say their pleasure is diminished or they no longer get as high, which decreases the desire for the drug.

In the case of the obesity vaccine, antibodies attach to the hunger protein called ghrelin, preventing it from reaching the brain and stimulating appetite.

To many researchers, the vaccines seem to be a potential answer to some of society’s major ills. In the U.S. there are 50 million cigarette smokers, 5 million drug addicts, 60 million obese adults and 9 million overweight youngsters between the ages of 6 and 19.

Most have one thing in common: They’d like to quit but can’t. Nearly seven out of 10 smokers, for instance, say they want to stop, but 80 percent to 90 percent of those who try to quit resume smoking within a year