Journal of Infectious Diseases Advance Access published March 26, 2014 1
Effectiveness of influenza vaccine against life‐threatening RT‐PCR‐confirmed influenza illness in US children, 2010‐2012
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Published by Oxford University Press on behalf of the Infectious Diseases Society of America 2014. This work is written by (a) US Government employee(s) and is in the public domain in the US.
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Jill M. Ferdinands1,2, Lauren E.W. Olsho3, Anna A. Agan4, Niranjan Bhat5, Ryan M. Sullivan4, Mark Hall6, Peter M. Mourani7, Mark Thompson1, Adrienne G. Randolph4, on behalf of the Pediatric Acute Lung Injury and Sepsis Investigators (PALISI) Network 1 Influenza Division, U.S. Centers for Disease Control and Prevention; Atlanta, GA 2 Battelle Memorial Institute; Atlanta, GA 3 Abt Associates, Inc.; Cambridge MA 4 Department of Anesthesia, Perioperative and Pain Medicine (Critical Care), Boston Children’s Hospital; Boston, MA 5 Johns Hopkins Bloomberg School of Public Health; Baltimore, MD 6 Division of Critical Care Medicine, Nationwide Children's Hospital; Columbus, OH 7 Section of Critical Care Medicine, Department of Pediatrics, University of Colorado School of Medicine and Children’s Hospital Colorado; Aurora, CO Corresponding author: Jill Ferdinands, PhD, US Centers for Disease Control and Prevention,
2 ABSTRACT Background: No studies have examined the effectiveness of influenza vaccine against ICU admission
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associated with influenza virus infection among children. Methods: In 2010‐11 and 2011‐12, children aged 6 months to 17 years admitted to 21 US pediatric
intensive care units (PICUs) with acute severe respiratory illness and testing positive for influenza were
enrolled as cases; children who tested negative were PICU controls. Community controls were children
without an influenza‐related hospitalization, matched to cases by comorbidities and geographic region.
Results: We analyzed data from 44 cases, 172 PICU controls, and 93 community controls. Eighteen percent of cases, 31% of PICU controls, and 51% of community controls were fully vaccinated.
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Compared to unvaccinated children, children who were fully vaccinated were 74% (95% CI, 19 to 91%) or 82% (95% CI, 23 to 96%) less likely to be admitted to a PICU for influenza compared to PICU controls or community controls, respectively. Receipt of one dose of vaccine among children for whom two
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doses were recommended was not protective.
Conclusion: During the 2010‐11 and 2011‐12 US influenza seasons, influenza vaccination was associated
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with a three‐quarters reduction in the risk of life‐threatening influenza illness in children.
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Vaccine effectiveness was estimated with logistic regression models.
3 INTRODUCTION One to 7 per 10,000 US children under the age of 18 years are hospitalized with laboratory‐
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confirmed influenza each year [1‐6]. Although most of these children require only standard care, 4% to 24% of children hospitalized with influenza‐related illness are admitted to an intensive care unit (ICU)
for life‐threatening complications [1, 2, 4, 7‐9]. Fifty to 60% of these children have pre‐existing chronic medical conditions [10, 11].
effectiveness of influenza vaccine against laboratory‐confirmed symptomatic and medically attended
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outpatient influenza illness among children [12‐27], although estimates of vaccine effectiveness (VE) vary by study and season, and fewer data are available on effectiveness of inactivated vaccine in
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children aged 6‐23 months [28]. Hadler et al. observed an 82% reduction in influenza hospitalization among children aged 3 to 9 years, but no reduction in influenza hospitalization among children