Original Articles
Does influenza vaccination prevent asthma exacerbations in children?*

https://doi.org/10.1067/mpd.2001.112168Get rights and content

Abstract

Objective: Influenza can exacerbate asthma, particularly in children. The effectiveness of influenza vaccine in preventing influenza-related asthma exacerbations, however, is not known. We evaluated influenza vaccine effectiveness in protecting children against influenza-related asthma exacerbations. Study design: We conducted a population-based retrospective cohort study with medical and vaccination records in 4 large health maintenance organizations in the United States during the 1993-1994, 1994-1995, and 1995-1996 influenza seasons. We studied children with asthma who were 1 through 6 years of age and who were identified by search of computerized databases of medical encounters and pharmacy dispensings. Main outcome measures were exacerbations of asthma evaluated in the emergency department or hospital. Results: Unadjusted rates of asthma exacerbations were higher after influenza vaccination than before vaccination. After adjustment was done for asthma severity by means of a self-control method, however, the incidence rate ratios of asthma exacerbations after vaccination were 0.78 (95% CI: 0.55 to 1.10), 0.59 (0.43 to 0.81), and 0.65 (0.52 to 0.80) compared with the period before vaccination during the 3 influenza seasons. Conclusions: After controlling for asthma severity, we found that influenza vaccination protects against acute asthma exacerbations in children. (J Pediatr 2001;138:306-10)

Section snippets

Methods

We conducted a retrospective cohort study with the Vaccine Safety Datalink, a computerized, linked database on immunizations, medical encounters, and demographic information.13 VSD contains data on more than 1,000,000 children enrolled in 4 large health maintenance organizations located on the West Coast of the United States. We analyzed 3 consecutive influenza seasons (October 1 through April 30) between 1993 and 1996. At the time of our analysis, data were available from 3 HMOs for the

Results

Depending on the influenza season, between 22,231 and 70,753 children with asthma were included in the analysis (Table I).

. Characteristics of children with asthma by influenza season, Vaccine Safety Datalink

Empty CellInfluenza season
1993-1994*1994-1995*1995-1996†
No. of children with asthma22,23138,66970,753
Sex
 Female, n (%)9,235 (41.5)16,115 (41.7)29,908 (42.3)
 Male, n (%)12,996 (58.5)22,554 (58.3)40,845 (57.7)
Age (y)
 1-2, n (%)6,845 (30.8)11,112 (28.7)18,712 (26.5)
 3-4, n (%)7,982 (35.9)14,419 (37.3)26,200

Discussion

We found that the apparent effectiveness of influenza vaccination against asthma exacerbations is highly confounded by asthma severity. In the traditional cohort analysis, in which vaccinated children were compared with unvaccinated children, we found that vaccination was associated with an increased risk of asthma exacerbations. Adjusting the cohort analysis for measures of asthma severity and other potential confounders decreased the relative risks, but risks remained significantly elevated.

Acknowledgements

Members of the Vaccine Safety Datalink Team:

Frank DeStefano MD, MPH, Robert T. Chen, MD, MA, John Glasser, PhD, MPH, Philip H. Rhodes, PhD, Steven Wassilak, MD, Piotr Kramarz, MD, Thomas Verstraeten, MD, Emmett Swint, MA, David Walker, MPH, Catherine Okoro, MS, Paul Gargiullo, PhD, Drew Baughman, MS, David King (National Immunization Program, Centers for Disease Control and Prevention, Atlanta, Georgia); Robert S. Thompson, MD, MPH, Robert L. Davis, MD, Lisa A. Jackson, MD, MPH, Patti Benson,

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    *

    Reprint requests: Frank DeStefano, MD, MPH, National Immunization Program, Centers for Disease Control and Prevention, 1600 Clifton Rd, MS-E61, Atlanta, GA 30333.

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