title: The effectiveness of influenza vaccination in preventing hospitalisation in children in Western Australia.
abstract: BACKGROUND
  There is increasing evidence demonstrating influenza vaccine effectiveness (VE) in the prevention of influenza in children, including the very young. Data demonstrating the effectiveness against severe disease, including hospitalisation, are limited. We aimed to determine the VE of the southern hemisphere trivalent inactivated influenza vaccine (TIV) in preventing laboratory-confirmed influenza-associated hospitalisation in children.
  
  
  METHODS
  Laboratory records were used to identify children with confirmed influenza hospitalised (i.e., cases) during a 5 year period (2008, 2010-2013) at the only tertiary paediatric facility in Western Australia. Cases and time, age and ward matched controls were retrospectively reviewed to determine risk factors, vaccination status and outcome. Adjusted odds ratios and VE estimates were derived using conditional logistic regression models.
  
  
  RESULTS
  Three hundred and eighty five cases were identified (Influenza A, 64.9%; Influenza B, 35.1%). Influenza-like illness and pneumonia were the most frequent presentation (74.5% and 23.9%, respectively). The median length of stay was 2 days (Interquartile range 1-4 days). Twenty children (5.2%) required admission to the intensive care unit. Vaccine uptake in cases and controls was low (4.9% and 8.5%, respectively). Three hundred and six case-control pairs were included in the VE analysis, of which 19 pairs were informative with discrepant vaccination status. VE (fully vaccinated vs. unvaccinated) was estimated to be 62.3% (95% CI: -6.6%, 86.7%).
  
  
  CONCLUSIONS
  In this study, the point estimate for the effectiveness of TIV in preventing influenza-associated hospitalisation in children was similar to that reported for emergency or outpatient attended, laboratory-confirmed influenza, yet confidence intervals were wide. Vaccine uptake remains low. Studies, enroling larger numbers of children, ideally with higher vaccine uptake, are needed to provide additional evidence on TIV protection against influenza hospitalisation in children.
authors.affiliation: School of Paediatrics and Child Health, University of Western Australia, Perth, Australia; Department of Infectious Diseases, Princess Margaret Hospital for Children, Perth, Australia; Department of Microbiology, PathWest Laboratory Medicine WA, Princess Margaret Hospital for Children, Perth, Australia; Wesfarmers Centre for Vaccines and Infectious Diseases, Telethon Kids Institute, University of Western Australia, Perth, Australia. Electronic address: christopher.blyth@uwa.edu.au.
authors.forename: Christopher C
authors.initials: CC
authors.lastname: Blyth
authors.affiliation: Infection Prevention and Healthcare Epidemiology Unit, Alfred Health, Department of Epidemiology and Preventive Medicine, Monash University, Melbourne, Australia.
authors.forename: Allen C
authors.initials: AC
authors.lastname: Cheng
authors.affiliation: Wesfarmers Centre for Vaccines and Infectious Diseases, Telethon Kids Institute, University of Western Australia, Perth, Australia.
authors.forename: Carolyn
authors.initials: C
authors.lastname: Finucane
authors.affiliation: Wesfarmers Centre for Vaccines and Infectious Diseases, Telethon Kids Institute, University of Western Australia, Perth, Australia.
authors.forename: Peter
authors.initials: P
authors.lastname: Jacoby
authors.affiliation: Communicable Disease Control Directorate, WA Department of Health, Perth, Australia.
authors.forename: Paul V
authors.initials: PV
authors.lastname: Effler
authors.affiliation: School of Pathology and Laboratory Medicine, University of Western Australia, Perth, Australia; Department of Microbiology, QEII Medical Centre, PathWest Laboratory Medicine WA, Perth, Australia.
authors.forename: David W
authors.initials: DW
authors.lastname: Smith
authors.affiliation: Victorian Infectious Diseases Reference Laboratory, Melbourne, Australia; Australian National University, Canberra, Australia.
authors.forename: Heath
authors.initials: H
authors.lastname: Kelly
authors.affiliation: National Centre for Immunisation Research and Surveillance of Vaccine Preventable Diseases, University of Sydney, Sydney, Australia; Children's Hospital Westmead, University of Sydney, Sydney, Australia.
authors.forename: Kristine K
authors.initials: KK
authors.lastname: Macartney
authors.affiliation: School of Paediatrics and Child Health, University of Western Australia, Perth, Australia; Wesfarmers Centre for Vaccines and Infectious Diseases, Telethon Kids Institute, University of Western Australia, Perth, Australia; Department of General Paediatrics, Princess Margaret Hospital for Children, Perth, Australia.
authors.forename: Peter C
authors.initials: PC
authors.lastname: Richmond
mesh_terms: D000293:Adolescent; D002648:Child; D002675:Child, Preschool; D005260:Female; D006760:Hospitalization; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D007252:Influenza Vaccines / Q000008:administration & dosage* / Q000276:immunology; D007251:Influenza, Human / Q000517:prevention & control*; D008297:Male; D012189:Retrospective Studies; D062606:Tertiary Care Centers; D016896:Treatment Outcome; D014611:Vaccination / Q000706:statistics & numerical data; D015164:Vaccines, Inactivated / Q000008:administration & dosage / Q000276:immunology; D014904:Western Australia / Q000453:epidemiology
chemical_list: D007252:Influenza Vaccines; D015164:Vaccines, Inactivated
keywords: Influenza; Influenza vaccine; Vaccine effectiveness