title: Seasonal influenza vaccine effectiveness in pre- and full-term children aged 6-23 months over multiple seasons.
abstract: BACKGROUND
  This study aimed to determine the effectiveness of seasonal influenza vaccine in pre- and full-term children aged 6-23 months.
  
  
  METHODS
  We examined a cohort of 683,354 young children (7.7% preterm) over five influenza seasons (2004-2005 to 2008-2009) in Ontario, Canada. Vaccine effectiveness was estimated using influenza-coded ambulatory visits during virologically-confirmed influenza season periods as the outcome and multivariable Cox proportional hazards modeling.
  
  
  RESULTS
  Full vaccination was associated with a 19% reduction in influenza-coded ambulatory visits (HR=0.81; 95% CI, 0.68-0.97) in all children, and an 18% reduction in full-term children (HR=0.82; 95% CI, 0.68-0.99). We did not find significant vaccine effectiveness for preterm children. No benefit was found for partial vaccination.
  
  
  CONCLUSIONS
  In children younger than two years, only full influenza vaccination is associated with reduced influenza-coded ambulatory visits. Since the effectiveness of influenza vaccination in preterm children remains uncertain, further study of this highly vulnerable population is warranted.
authors.affiliation: Dalla Lana School of Public Health, University of Toronto, Toronto, Canada.
authors.forename: Shixin
authors.initials: S
authors.lastname: Shen
authors.forename: Michael A
authors.initials: MA
authors.lastname: Campitelli
authors.forename: Andrew
authors.initials: A
authors.lastname: Calzavara
authors.forename: Astrid
authors.initials: A
authors.lastname: Guttmann
authors.forename: Jeffrey C
authors.initials: JC
authors.lastname: Kwong
mesh_terms: D000553:Ambulatory Care / Q000706:statistics & numerical data; D015331:Cohort Studies; D005260:Female; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D007234:Infant, Premature; D007252:Influenza Vaccines / Q000008:administration & dosage / Q000276:immunology*; D007251:Influenza, Human / Q000453:epidemiology* / Q000276:immunology / Q000517:prevention & control*; D008297:Male; D009864:Ontario / Q000453:epidemiology; D012621:Seasons; D014611:Vaccination
chemical_list: D007252:Influenza Vaccines