Question

• Does influenza vaccination prevent asthma exacerbations in children?

Clinical Bottom Lines

1. Influenza vaccination is associated with a decrease in the rate of asthma exacerbation in children age 1-6 years.¹
   
2. There is now evidence to support the AAP recommendation that children with asthma be vaccinated for influenza annually.²

Summary of Key Evidence

1.  A population-based, retrospective cohort study using the Vaccine Safety Datalink database showed that the risk of asthma exacerbations in children age 1-6 years decreased following influenza vaccination by 22%(95%CI; -10-45%), 41%(19-57%), and 35%(19-57%) for three consecutive influenza seasons.¹
2.  The unadjusted asthma exacerbation rates were higher following vaccination due to confounding by severity, i.e. patients with more severe asthma were more likely to be vaccinated.1
3.  Adjustment by means of a self-control analysis was required to account for the confounding effects of asthma severity.1
4. The self-control analysis required that each patient have at least one emergency visit/hospitalization and, therefore, the conclusions are limited to patients with severe or poorly controlled asthma.

Additional Comments

• In this example of a self-control analysis, the incidence of asthma exacerbations prior to vaccination is compared to the incidence after vaccination for
  the same child. This approach is analogous to a cross-over design in a clinical trial, where each child serves as his/her own control.
• Limitations to this retrospective, non-experimental design are numerous. In this example, the results could be strongly biased by more aggressive asthma therapy post-vaccination since, by definition, each patient would have had multiple exacerbations by the end of the study period.³
• Despite the limitations of this study, it provides the first evidence to support influenza vaccination in an important group of high-risk pediatric patients. This is especially so since a randomized controlled trial designed to address this question may not be ethical.

Citation

1. Kramarz P, DeStefano F, Gargiullo PM, Chen RT, Lieu TA, Davis RL, Mullooly JP, Black SB, Shinefield HR, Boblke K, Ward JI, Marcy SM, and the Vaccine Safety Datalink Team. Does influenza vaccination prevent asthma exacerbations in children? J Pediatr 2001;138:306-310.
2. American Academy of Pediatrics. Influenza. In: Pickering LK, editor. 2000 Red Book: Report of the Committee on Infectious Diseases 25th ed. Elk Grove Village (IL): American Academy of Pediatrics; 2000. p. 356.
3. Neuzil KM. Influenza vaccine in children with asthma: Why no progress? J Pediatr 2001;138:301-303.

CAT Author: Damian J. Krysan MD, Ph.D.

CAT Appraisers: John Frohna, MD, MPH

Date appraised: October 22, 2001