Contrary to widespread fears among patients and some doctors, flu shots are safe even for those with severe asthma, a study found.

Many people with asthma believe getting the vaccine – as health officials recommend – can cause dangerous asthma attacks.

Because of that misconception, only about 10 percent of asthma patients get a flu shot each year, said the study’s lead author, Dr. Mario Castro of Washington University School of Medicine in St. Louis.

Castro and researchers at 18 other sites around the country put those fears to the test by studying 2,032 children and adults with asthma.

Maine, which has the nation’s highest adult asthma rate, participated in the study.

Half the patients got a flu vaccination and the other half an inactive shot. They were checked for symptoms for two weeks. After another week, the groups were switched, so everyone got the vaccine at some point.

After both the real and dummy shots, about three in 10 people had an asthma flare-up, with breathing difficulty. Asthma patients often suffer flare-ups because of colds, exercise or exposure to irritants such as pollen, animal dander, smoke, dust mites and cold air.

“Now we know for the first time that this is safe to use in all asthmatics,” Castro said.

Linda C. Lambert, influenza program officer at the National Institute of Allergy and Infectious Diseases, said the study sends a strong message that the vaccine is safe for asthmatics. “I hope physicians will take notice of this and recommend that their patients get flu shots,” she said.

The research was reported in Thursday’s New England Journal of Medicine.

The Centers for Disease Control and Prevention recommends all asthma patients – plus those with other chronic respiratory conditions or weak immune systems – get an annual flu shot.

Each year, flu kills 20,000 to 40,000 Americans and sends many more to the hospital or bed.

The prevalence of asthma has been rising in this country, and deaths jumped 109 percent from 1979 to 1998, when asthma killed 5,438 people.