Infection with influenza can lead to diverse respiratory complications and might result in a substantial burden on the health system. However, influenza accounted for only 0% to 7% of viral-induced asthma exacerbations,2,8
and evidence for a specific additional risk in children with asthma is lacking.
Can influenza vaccination directly reduce the number of asthma exacerbations? Studies in recent years resulted in contradictory outcomes.9–11
In a retrospective cohort study during 3 consecutive influenza seasons, Kramarz et al used computerized databases of 4 large health maintenance organizations in the United States to evaluate the effectiveness of influenza vaccinations in children with asthma aged 1 to 6 years old. Unadjusted rates of asthma exacerbations were higher in the vaccinated group, and after adjustment for asthma severity and other confounding factors, the vaccine was found to reduce the risk of asthma exacerbation by 22% to 41%.9
In another retrospective study in children 0 to 12 years old with asthma, a beneficial clinical effect (reduction in number of lower respiratory tract infections and acute otitis media) was identified in vaccinated preschool children.10
Ong et al reported a reduction in the use of oral steroids in vaccinated children with asthma.11
While these results are of interest, some limitations such as lack of adjustment for asthma severity and recall bias should be considered.
One randomized, double-blind, placebo-controlled trial conducted in the Netherlands aimed to answer the question of whether influenza vaccination was more effective than placebo in preventing asthma exacerbations. Children 6 to 18 years of age with asthma received either inactivated influenza vaccine (349 children) or placebo (347 children). The children were followed throughout influenza season, and pharyngeal swabs for detection of influenza virus were obtained during asthma exacerbations. This study failed to demonstrate a difference between the intervention and the control groups; there was no effect of influenza vaccination on the number or severity of influenza-related asthma exacerbations.12
Further analysis of questionnaires and patient diaries found influenza vaccination to improve health-related quality of life, but when compared with placebo, respiratory symptoms and spirometric parameters during all seasons were similar.13
Moreover, only 1.8% of all asthma exacerbations were influenza related, indicating the relatively small effect of this virus on the overall exacerbation rate in children with asthma.