title: The effectiveness of influenza vaccination in preventing hospitalizations in children in Hong Kong, 2009-2013.
abstract: BACKGROUND
  Influenza vaccination is widely recommended every year to protect individuals against influenza virus infection and illness. There are few published estimates of influenza vaccine effectiveness against hospitalization in children or from subtropical regions.
  
  
  METHODS
  We conducted a test-negative year-round study between October 2009 and September 2013, recruiting children 6 months to 17 years of age admitted to two hospitals in Hong Kong with a febrile acute respiratory infection. Cases were tested for influenza A and B and conditional logistic regression was used to estimate vaccine effectiveness comparing influenza vaccination history of the trivalent influenza vaccine (TIV) among patients testing positive versus negative for influenza, adjusting for age and sex and matching by calendar week of recruitment.
  
  
  RESULTS
  Overall vaccine effectiveness against hospitalization with laboratory-confirmed influenza A and B was estimated to be 61.7% (95% CI: 43.0%, 74.2%). The estimated vaccine effectiveness against A(H3N2) was 36.6% (95% CI: -25.5%, 67.9%) compared to 71.5% (95% CI: 39.4%, 86.6%) for A(H1N1)pdm09 and 68.8% (95% CI: 41.6%, 83.3%) for B.
  
  
  CONCLUSIONS
  Vaccine effectiveness against hospitalization in children varied from year to year, but was moderate to high overall even in an area with influenza activity throughout the year.
authors.affiliation: Division of Epidemiology and Biostatistics, School of Public Health, The University of Hong Kong, Hong Kong Special Administrative Region, China.
authors.forename: Benjamin J
authors.initials: BJ
authors.lastname: Cowling
authors.affiliation: Department of Microbiology, The University of Hong Kong, Hong Kong Special Administrative Region, China.
authors.forename: Kwok-Hung
authors.initials: KH
authors.lastname: Chan
authors.affiliation: Division of Epidemiology and Biostatistics, School of Public Health, The University of Hong Kong, Hong Kong Special Administrative Region, China.
authors.forename: Shuo
authors.initials: S
authors.lastname: Feng
authors.affiliation: Department of Pediatrics and Adolescent Medicine, The University of Hong Kong, Hong Kong Special Administrative Region, China.
authors.forename: Eunice L Y
authors.initials: EL
authors.lastname: Chan
authors.affiliation: Public Health Laboratory Services Branch, Centre for Health Protection, Department of Health, Hong Kong Special Administrative Region, China.
authors.forename: Janice Y C
authors.initials: JY
authors.lastname: Lo
authors.affiliation: Division of Public Health Laboratory Sciences, School of Public Health, The University of Hong Kong, Hong Kong Special Administrative Region, China; Centre for Influenza Research, The University of Hong Kong, Hong Kong Special Administrative Region, China.
authors.forename: J S Malik
authors.initials: JS
authors.lastname: Peiris
authors.affiliation: Department of Pediatrics and Adolescent Medicine, The University of Hong Kong, Hong Kong Special Administrative Region, China. Electronic address: ssschiu@hkucc.hku.hk.
authors.forename: Susan S
authors.initials: SS
authors.lastname: Chiu
mesh_terms: D000293:Adolescent; D002648:Child; D002675:Child, Preschool; D005260:Female; D006723:Hong Kong / Q000453:epidemiology; D006760:Hospitalization / Q000706:statistics & numerical data*; D006801:Humans; D007223:Infant; D007252:Influenza Vaccines / Q000627:therapeutic use*; D007251:Influenza, Human / Q000453:epidemiology* / Q000517:prevention & control; D016015:Logistic Models; D008297:Male; D014611:Vaccination / Q000706:statistics & numerical data
chemical_list: D007252:Influenza Vaccines
keywords: Children; Effectiveness; Hospitalization; Influenza; Vaccine
references.citation: N Engl J Med. 2014 Feb 27;370(9):789-91
references.pmid: 24450860
references.citation: N Engl J Med. 2013 Dec 26;369(26):2481-91
references.pmid: 24328444
references.citation: Int J Epidemiol. 2007 Jun;36(3):623-31
references.pmid: 17403908
references.citation: Euro Surveill. 2013 Jan 31;18(5):
references.pmid: 23399424
references.citation: Euro Surveill. 2013 Jan 31;18(5):
references.pmid: 23399423
references.citation: Vaccine. 2011 Oct 6;29(43):7320-5
references.pmid: 21810450
references.citation: Vaccine. 2013 Apr 19;31(17):2165-8
references.pmid: 23499601
references.citation: Vaccine. 2012 Dec 17;31(1):49-57
references.pmid: 23142300
references.citation: Euro Surveill. 2013 Jan 31;18(5):
references.pmid: 23399425
references.citation: PLoS One. 2013;8(3):e58222
references.pmid: 23472161
references.citation: Epidemiology. 2012 Nov;23(6):930-1
references.pmid: 23038121
references.citation: J Virol. 2005 Jan;79(2):884-95
references.pmid: 15613317
references.citation: J Clin Virol. 2008 May;42(1):65-9
references.pmid: 18242124
references.citation: PLoS One. 2013 Jul 16;8(7):e68760
references.pmid: 23874754
references.citation: J Infect Dis. 2009 Jan 15;199(2):168-79
references.pmid: 19086914
references.citation: Postgrad Med J. 2010 Sep;86(1019):515-21
references.pmid: 20693151
references.citation: J Infect Dis. 2012 Jun 15;205(12):1858-68
references.pmid: 22492921
references.citation: Am J Epidemiol. 2013 Apr 15;177(8):834-40
references.pmid: 23459950
references.citation: N Engl J Med. 2010 Jun 10;362(23):2175-2184
references.pmid: 20558368
references.citation: Clin Infect Dis. 2012 Jun;54(12):1778-83
references.pmid: 22423139
references.citation: Vaccine. 2013 Jun 26;31(30):3104-9
references.pmid: 23624093
references.citation: Clin Infect Dis. 2009 Oct 1;49(7):1016-21
references.pmid: 19722912
references.citation: Vaccine. 2012 Feb 27;30(10):1895-900
references.pmid: 22222872
references.citation: Emerg Infect Dis. 2005 Nov;11(11):1738-41
references.pmid: 16318726
references.citation: Lancet Infect Dis. 2012 Jan;12(1):36-44
references.pmid: 22032844
references.citation: N Engl J Med. 2002 Dec 26;347(26):2097-103
references.pmid: 12501221
references.citation: Pediatrics. 2014 May;133(5):e1218-25
references.pmid: 24753525
references.citation: J Med Virol. 2014 Jun;86(6):1017-25
references.pmid: 24395730
references.citation: Clin Infect Dis. 2014 Feb;58(3):319-27
references.pmid: 24235265
references.citation: Vaccine. 2011 Mar 21;29(14):2613-8
references.pmid: 21292008
references.citation: J Clin Microbiol. 2007 Nov;45(11):3655-64
references.pmid: 17804649
references.citation: Pediatrics. 2008 Nov;122(5):911-9
references.pmid: 18977968
references.citation: Influenza Other Respir Viruses. 2011 Sep;5(5):299-305
references.pmid: 21668694
references.citation: Influenza Other Respir Viruses. 2013 Nov;7(6):1175-80
references.pmid: 24103037
references.citation: J Infect Dis. 2014 Jul 1;210(1):126-37
references.pmid: 24446529
references.citation: Clin Infect Dis. 2013 Sep;57(6):789-93
references.pmid: 23748138
references.citation: J Infect. 2014 Apr;68(4):363-71
references.pmid: 24291062
references.citation: J Clin Microbiol. 2008 Jul;46(7):2195-9
references.pmid: 18463206
references.citation: PLoS Med. 2008 Mar 25;5(3):e74
references.pmid: 18366252