title: Effectiveness of trivalent flu vaccine in healthy young children.
abstract: BACKGROUND
  There are few studies evaluating the effectiveness of trivalent influenza vaccination (TIV) in young children, particularly in children <2 years. The Western Australian Influenza Vaccine Effectiveness Study commenced in 2008 to evaluate a program providing TIV to children aged 6 to 59 months.
  
  
  METHODS
  An observational study enrolling children with influenza-like illness presenting to a tertiary pediatric hospital was conducted (2008-2012). Vaccination status was determined by parental questionnaire and confirmed via the national immunization register and/or vaccine providers. Respiratory virus polymerase chain reaction and culture were performed on nasopharyngeal samples. The test-negative design was used to estimate vaccine effectiveness (VE) by using 2 control groups: all influenza test-negative subjects and other-virus-detected (OVD) subjects. Adjusted odds ratios were estimated from models with season, month of disease onset, age, gender, indigenous status, prematurity, and comorbidities as covariates. Subjects enrolled in 2009 were excluded from VE calculations.
  
  
  RESULTS
  Of 2001 children enrolled, influenza was identified in 389 (20.4%) children. Another respiratory virus was identified in 1134 (59.6%) children. Overall, 295 of 1903 (15.5%) children were fully vaccinated and 161 of 1903 (8.4%) children were partially vaccinated. Vaccine uptake was significantly lower in 2010-2012 after increased febrile adverse events observed in 2010. Using test-negative controls, VE was 64.7% (95% confidence interval [CI]: 33.7%-81.2%). No difference in VE was observed with OVD controls (65.8%; 95% CI: 32.1%-82.8%). The VE for children <2 years was 85.8% (95% CI: 37.9%-96.7%).
  
  
  CONCLUSIONS
  This study reveals the effectiveness of TIV in young children over 4 seasons by using test-negative and OVD controls. TIV was effective in children aged <2 years. Despite demonstrated vaccine effectiveness, uptake of TIV remains suboptimal.
authors.affiliation: School of Paediatrics and Child Health and Princess Margaret Hospital for Children, Perth, Australia; Telethon Institute of Child Health Research, West Perth, Australia; PathWest Laboratory Medicine, Nedlands, Australia; christopher.blyth@uwa.edu.au.
authors.forename: Christopher C
authors.initials: CC
authors.lastname: Blyth
authors.affiliation: Telethon Institute of Child Health Research, West Perth, Australia;
authors.forename: Peter
authors.initials: P
authors.lastname: Jacoby
authors.affiliation: Communicable Disease Control Directorate, Department of Health, Perth, Australia;
authors.forename: Paul V
authors.initials: PV
authors.lastname: Effler
authors.affiliation: Victorian Infectious Diseases Reference Laboratory, Melbourne, Australia; and Australian National University, Australian Capital Territory, Australia.
authors.forename: Heath
authors.initials: H
authors.lastname: Kelly
authors.affiliation: PathWest Laboratory Medicine, Nedlands, Australia; School of Pathology and Laboratory Medicine, University of Western Australia, Perth, Australia;
authors.forename: David W
authors.initials: DW
authors.lastname: Smith
authors.affiliation: Telethon Institute of Child Health Research, West Perth, Australia;
authors.forename: Christine
authors.initials: C
authors.lastname: Robins
authors.affiliation: Telethon Institute of Child Health Research, West Perth, Australia;
authors.forename: Gabriela A
authors.initials: GA
authors.lastname: Willis
authors.affiliation: PathWest Laboratory Medicine, Nedlands, Australia;
authors.forename: Avram
authors.initials: A
authors.lastname: Levy
authors.affiliation: PathWest Laboratory Medicine, Nedlands, Australia;
authors.forename: Anthony D
authors.initials: AD
authors.lastname: Keil
authors.affiliation: School of Paediatrics and Child Health and Princess Margaret Hospital for Children, Perth, Australia; Telethon Institute of Child Health Research, West Perth, Australia;
authors.forename: Peter C
authors.initials: PC
authors.lastname: Richmond
mesh_terms: D000914:Antibodies, Viral / Q000097:blood; D002675:Child, Preschool; D005260:Female; D006801:Humans; D007117:Immunization, Secondary; D007223:Infant; D007252:Influenza Vaccines / Q000008:administration & dosage* / Q000276:immunology*; D007251:Influenza, Human / Q000276:immunology* / Q000517:prevention & control*; D008297:Male; D016896:Treatment Outcome; D014904:Western Australia
chemical_list: D000914:Antibodies, Viral; D007252:Influenza Vaccines
keywords: children; influenza; trivalent influenza vaccine; vaccine effectiveness