title: Lessons from the first year of the WAIVE study investigating the protective effect of influenza vaccine against laboratory-confirmed influenza in hospitalised children aged 6-59 months.
abstract: BACKGROUND
  Influenza is major cause of paediatric hospitalisation. Influenza vaccine was offered to all children aged 6-59 months resident in Western Australia in 2008, and we wished to evaluate the effectiveness of this immunisation programme.
  
  
  OBJECTIVE
  To assess the practicalities of a nested matched case-control design to estimate the protective effect of inactivated influenza vaccination in hospitalised children aged 6-59 months.
  
  
  METHODS
  Cases were hospitalised children with laboratory-confirmed influenza, while matched controls were recruited from children admitted for an acute non-respiratory illness. We estimated influenza vaccine effectiveness (VE) against influenza as 1--the adjusted odds ratio from multivariate logistic regression.
  
  
  RESULTS
  The 2008 influenza season was characterised by a late peak and a predominance of influenza virus B. We recruited 26 hospitalised patients with laboratory-confirmed influenza and 50 matched controls. The proportion of cases who were fully vaccinated was 7% versus 30% of controls giving an adjusted VE of 83% (95% CI--54 to 98).
  
  
  CONCLUSIONS
  Recruiting sufficient controls was problematic and in the future, we will select controls hospitalised for an influenza-like-illness but influenza negative by laboratory PCR testing. The VE estimate was high but non-significant, reflecting the low number of cases.
authors.affiliation: Telethon Institute for Child Health Research, Centre for Child Health Research, University of Western Australia, Australia.
authors.forename: Gabriela A
authors.initials: GA
authors.lastname: Dixon
authors.forename: Hannah C
authors.initials: HC
authors.lastname: Moore
authors.forename: Heath
authors.initials: H
authors.lastname: Kelly
authors.forename: Peter
authors.initials: P
authors.lastname: Jacoby
authors.forename: Dale
authors.initials: D
authors.lastname: Carcione
authors.forename: Simon
authors.initials: S
authors.lastname: Williams
authors.forename: David
authors.initials: D
authors.lastname: Smith
authors.forename: Anthony D
authors.initials: AD
authors.lastname: Keil
authors.forename: Paul
authors.initials: P
authors.lastname: Van Buynder
authors.forename: Peter C
authors.initials: PC
authors.lastname: Richmond
mesh_terms: D000367:Age Factors; D016022:Case-Control Studies; D002675:Child, Preschool; D005260:Female; D006760:Hospitalization / Q000706:statistics & numerical data*; D006801:Humans; D017589:Immunization Programs / Q000379:methods*; D007223:Infant; D053118:Influenza A Virus, H1N1 Subtype / Q000276:immunology / Q000302:isolation & purification; D053122:Influenza A Virus, H3N2 Subtype / Q000276:immunology / Q000302:isolation & purification; D009981:Influenza B virus / Q000276:immunology / Q000302:isolation & purification; D007252:Influenza Vaccines / Q000008:administration & dosage* / Q000276:immunology; D007251:Influenza, Human / Q000453:epidemiology* / Q000276:immunology / Q000517:prevention & control* / Q000821:virology; D016015:Logistic Models; D008297:Male; D016017:Odds Ratio; D015397:Program Evaluation; D016896:Treatment Outcome; D014904:Western Australia / Q000453:epidemiology
chemical_list: D007252:Influenza Vaccines