• Marieke L A de Hoog, Roderick P Venekamp, Damoiseaux Roger A M J RAMJ Julius Center for Health Sciences and Primary Care, University Medical Center, Utrecht University, The Netherlands., Schilder Anne G M AGM Julius Center for Health Sciences and Primary Care, University Medical Center, Utrecht University, The Netherlands. , Sanders Elisabeth A M EAM Wilhelmina Children's Hospital, University Medical Center, Utrecht University, The Netherlands. , Henriette A Smit, and Patricia C J L Bruijning-Verhagen.
• Julius Center for Health Sciences and Primary Care, University Medical Center, Utrecht University, The Netherlands m.l.a.dehoog@umcutrecht.nl.
• Ann Fam Med. 2019 Jan 1; 17 (1): 7-13.

PurposeAnnual influenza immunization in medical risk groups is recommended in many countries. Recent evidence suggests that repeated inactivated influenza vaccine (IIV) immunization throughout childhood may impair long-term immunity against influenza. We assessed whether prior immunization altered the effect of IIV in children with preexisting medical conditions on primary care-diagnosed respiratory illness (RI) episodes during the influenza season.MethodsElectronic records of IIV-immunized children who met the criteria for annual IIV immunization according to Dutch guidelines were extracted from a primary care database from 2004 to 2015. For each year, we collected information on IIV immunization status, primary care-attended RI episodes (including influenza-like illness, acute RI, and asthma exacerbation), and potential confounders. Generalized estimating equations were used to model the association between prior IIV and occurrence of at least one RI episode during the influenza season, with "current year immunized but without IIV history" as reference group.ResultsA total of 4,183 children (follow-up duration: 11,493 child-years) were IIV immunized at least once. Adjusted estimates showed lower odds for RI in current year-immunized children with prior IIV compared with those without (odds ratio [OR] = 0.61; 95% CI, 0.47-0.78 for "current year immunized and one IIV in previous 2 years"; OR = 0.85; 95% CI, 0.68-1.07 for "current year immunized and ≥2 IIVs in previous 3 years, including prior year").ConclusionRepeated IIV immunization in children with preexisting medical conditions has no negative impact on, and may even increase, long-term protection against RI episodes diagnosed during the influenza season in primary care.© 2019 Annals of Family Medicine, Inc.

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