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. 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. "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 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. 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.