May 19 (HealthDay News) -- Children who get the annual flu vaccine, especially those who have asthma, may be more likely to be hospitalized than children who don't get the shot, a new study shows.
But the researcher noted that the surprise finding probably has more to do with the severity of the underlying illness in children receiving the vaccine than with any deficiency in the vaccine.
"This may not be a reflection of the vaccine but that these patients are the sickest, and their doctors insist they get a vaccination," said study author Dr. Avni Y. Joshi, a fellow at the Mayo Clinic in Rochester, Minn. She is to present her findings Tuesday at the American Thoracic Society's annual meeting, in San Diego.
Other experts came to similar conclusions about the finding.
"I would be very cautious about interpreting this," said Dr. Gurjit Khurana Hershey, director of asthma research and professor of pediatrics at Cincinnati Children's Hospital. "The bottom line is that kids with asthma who get the flu vaccine are probably a different population anyway. They may be the more severely ill children, so it may have very little to do with the vaccine."
The study has too many unknowns and covers too wide an age range over too many flu seasons to indicate any change in recommendations, said Dr. Hank Bernstein, a member of the committee on infectious diseases of the American Academy of Pediatrics and a professor of pediatrics at Dartmouth Medical School.
"We know that the efficacy of the vaccine can be limited in younger children," he said. "The current recommendations are to immunize all children 6 months through 18 years. Household contacts and out-of-home caregivers of all healthy children under 5 years of age, and children with a chronic medical condition that puts them at increased risk of complications from the flu should also get the vaccine every year."
Children aged 2 to 18 years can get either the injected trivalent inactivated influenza vaccine (TIV) or the live attenuated influenza vaccine (LAIV), given in the form of a nasal spray. Children under 2 should get only TIV, he added.
"Previous research has shown that the TIV does not provoke asthma attacks, but we've yet to see how effective it is in reducing hospitalization rates associated with the seasonal flu," Joshi said.
The authors looked back at 263 children aged 6 months to 18 years who had visited the Mayo Clinic between 1999 and 2006 with laboratory-confirmed influenza.
Children -- including children who had asthma -- who received the annual inactivated flu vaccine were almost three times more likely to be hospitalized than those who were not inoculated.
There is no reason to believe the vaccine actually caused the hospitalizations, Joshi emphasized. This could simply mean that the shot isn't effective in preventing hospital stays.
"The flu shot may be safer in terms of triggering a wheezing episode, but we don't know how effective it is. We need more studies to assess the effectiveness of different kinds of vaccines. There could be something that has higher efficacy not only in preventing influenza illness, but also hospitalizations," she said.
"Vaccination should be universal, but we may need to find more effective vaccines," Joshi added. "This is a good vaccine. We could have better."
SOURCES: Avni Y. Joshi, M.D., fellow, allergy, immunology and infectious diseases, Mayo Clinic, Rochester, Minn.; Gurjit Khurana Hershey, M.D., Ph.D., director, Division of Asthma Research, Cincinnati Children's Hospital; Hank Bernstein, D.O., member, committee on infectious diseases, American Academy of Pediatrics, and professor, pediatrics, Dartmouth Medical School; May 19, 2009, presentation, American Thoracic Society annual meeting, San Diego