MedWire News: Children with asthma who receive the flu vaccine may be more likely to be hospitalized with influenza than their unvaccinated counterparts, US researchers believe.

They said that their discovery raises doubts about the efficacy of the vaccine in asthmatic children, but admit it could also reflect the population of children who are likely to be vaccinated.

The study, which was presented at the American Thoracic Society International Conference in San Diego, California, USA, focused on the efficacy of the trivalent inactivated flu vaccine (TIV) in children. The US authorities currently recommend annual vaccination of all children with the TIV.

Avni Joshi (Mayo Clinic, Rochester, Minnesota) and colleagues identified all patients at the Mayo Clinic aged 6 months to 18 years who had laboratory-confirmed influenza during each flu season from 1999 to 2006. These 236 cases were classified according to their asthma status, receipt of the TIV, and whether they had an influenza-related hospitalization.

Vaccinated children were nearly three times as likely to be hospitalized as children who had not received the vaccine (odds ratio 2.97), Joshi et al calculated. In the subset of children with asthma, the risk of hospitalization was significantly higher among vaccinated versus unvaccinated children.

Other factors, such as asthma severity and insurance plans, did not affect the risk for hospitalization, however.

The researchers concluded that the TIV does not appear to provide protection against hospitalization in pediatric patients, including those with asthma.

“While these findings do raise questions about the efficacy of the vaccine, they do not in fact implicate it as a cause of hospitalizations,” Joshi said. “More studies are needed to assess not only the immunogenicity but also the efficacy of different influenza vaccines in asthmatic subjects.”

MedWire (www.medwire-news.md) is an independent clinical news service provided by Current Medicine Group, a part of Springer Science+Business Media. © Current Medicine Group Ltd; 2009

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