ATLANTA — Health officials are warning that the whooping cough vaccine doesn’t last a lifetime — as an outbreak in Vermont demonstrated last year.

The outbreak had 290 people hacking, almost half of them teen-agers.

“The vaccine is highly effective for early childhood years, but it may wane over time,” Dr. Dalya Guris, an epidemiologist with the Centers for Disease Control and Prevention, said Thursday.

Five doses of whooping cough vaccine by age 7 are recommended for maximum protection. After that, no booster shots or catch-up vaccines have been approved in the United States.

The CDC said doctors must keep close watch for the symptoms in adults. Antibiotics work when used early.

The outbreak gave Vermont a higher rate of whooping cough in 1996 than any other state — 48 cases per 100,000 people. The national rate was about 3 cases per 100,000 people.

Those who became ill in Vermont ranged in age from infancy to 87. The CDC said 15 percent were ages 5 to 9, while 46 percent were 10 to 19 and 23 percent were 20 and older. More than half of the patients between 7 and 18 had received four or more doses of the vaccine.

Whooping cough gets its name from the “whoop” children make when trying to breathe between coughs. It typically kills five to 10 people a year in the United States, mostly unvaccinated children.