As any smoker can tell you, quitting is relatively easy. The hard part is avoiding relapse—the urge to light up weeks or even months after you have supposedly kicked the habit. The patch, the gum and all the other tricks smokers use to get through the first few months are often powerless against those later urges.

That is one reason why an antinicotine vaccine now wending its way through clinical trials has public health officials so excited. Like all vaccines, NicVAX, made by NABI Biopharmaceuticals, works by stimulating the body’s immune system to produce antibodies against a certain target—in this case, nicotine. Because immune responses are generally lifelong, the vaccine makers say it could serve as a long-term antismoking aid.

Normally nicotine molecules are small enough to evade detection by the immune system. They are even small enough to slip past the blood-brain barrier and bind to receptors on brain cells, where they trigger a chemical cascade that leads to addiction. NicVAX floods the body with nicotine molecules that have been chemically attached to large, carrier proteins, forcing the immune system to recognize and deploy antibodies against the cigarette ingredient. Then, when ordinary nicotine molecules enter the system, those antibodies bind to them, making them too large to cross the blood-brain barrier.  

The vaccine doesn’t work for everyone. An earlier trial showed that 16 percent of heavy smokers who were vaccinated and had high antibody levels remained abstinent from cigarettes one year after quitting, compared with 6 percent of the placebo group. Those who produced high antibodies but did not quit cut their smoking in half, from around 20 cigarettes a day to 10.

Results from wider, or “phase III,” trials are expected as early as September. For these studies, researchers recruited 1,000 smokers who consume at least 10 cigarettes a day. The volunteers received five to six injections spaced roughly one month apart and were asked to quit after 14 weeks, when around 80 percent of subjects have high antibody levels. (Why 20 percent of subjects fail to produce a high antibody response to the vaccine is unclear.). “The idea is to ensure that when we tell them to quit, they have the tools—the antibodies—to help them,” says NABI CEO Raafat E. F. Fahim. He and his team have yet to determine how long patients will need to get shots.

If results from the phase III trials are as good as everyone expects, the vaccine could hit pharmacy shelves soon after. Meanwhile researchers are already at work on other antiaddiction vaccines, including one against cocaine that employs the same strategy as NicVAX.