title: Hospital-based vaccine effectiveness against influenza B lineages, Hong Kong, 2009-14.
abstract: BACKGROUND
  We estimated vaccine effectiveness (VE) against pediatric influenza B hospitalizations in Hong Kong year round between November 2001 and October 2014.
  
  
  METHODS
  We conducted a test-negative year-round study, enrolling children 6 months to 17 years of age admitted to two hospitals in Hong Kong with a febrile acute respiratory infection. Children were tested for influenza A and B. Conditional logistic regression was used to estimate overall and lineage-specific vaccine effectiveness comparing influenza vaccination history of the trivalent influenza vaccine (TIV) among patients testing positive for influenza B versus negative for influenza A and B, adjusting for age and sex and matching by calendar week of recruitment.
  
  
  RESULTS
  Of the 6013 children included in the analysis, 262 tested positive for influenza B. Vaccination coverage was low: 6.5% in the influenza B positive children when compared with 8.8% in children who tested negative for both influenza A and B (p=0.248). Overall, VE was 47.6% (95% CI: 10.0, 69.4%) against influenza B hospitalization despite variable co-circulation of both lineages in all years. VE for Victoria-like virus calculated from 3 years when the vaccine was lineage-matched was 59.1% (95% CI: 6.2, 82.2%). Lineage-matched VE for Yamagata-like virus was -8.8% (95% CI: -215.4, 62.5%) in a clade mismatch season. With wide confidence intervals, we were unable to demonstrate cross-lineage protection: VE against the mismatched B/Yamagata-like virus was 9.5% (95% CI: -240.4, 76.0%) in 2011/12 and against mismatched B/Victoria-like virus in 2013/14 was 42.7% (95% CI: -368.6, 93.0%).
  
  
  CONCLUSIONS
  TIV conferred an overall VE of 47.6% (95% CI: 10.0, 69.4%) against influenza B hospitalization in children despite variable co-circulation of both lineages in all years. Lineage-matched VE for Yamagata-like virus was poor and may be related to clade mismatch. Cross-lineage protection was not observed.
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
authors.affiliation: WHO Collaborating Centre for Infectious Disease Epidemiology and Control, 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 Microbiology, The University of Hong Kong, Hong Kong Special Administrative Region, China.
authors.forename: Kwok-Hung
authors.initials: KH
authors.lastname: Chan
authors.affiliation: Public Health Laboratory Services Branch, Centre for Health Protection, Department of Health, China.
authors.forename: Janice Y C
authors.initials: JY
authors.lastname: Lo
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: Department of Pediatrics and Adolescent Medicine, Pamela Youde Nethersole Eastern Hospital, Chai Wan, Hong Kong Special Administrative Region, China.
authors.forename: Lok-Yee
authors.initials: LY
authors.lastname: So
authors.affiliation: WHO Collaborating Centre for Infectious Disease Epidemiology and Control, 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: WHO Collaborating Centre for Infectious Disease Epidemiology and Control, School of Public Health, The University of Hong Kong, Hong Kong Special Administrative Region, China; Centre of Influenza Research, The University of Hong Kong, Hong Kong Special Administrative Region, China.
authors.forename: J S Malik
authors.initials: JS
authors.lastname: Peiris
mesh_terms: D000293:Adolescent; D002648:Child; D002675:Child, Preschool; D056738:Cross Protection; D005260:Female; D006723:Hong Kong / Q000453:epidemiology; D006760:Hospitalization / Q000706:statistics & numerical data*; D006761:Hospitals; D006801:Humans; D007223:Infant; D009981:Influenza B virus; 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; Hospitalization; Influenza B; Lineage specific; Triavalent influenza vaccine; Vaccine effectiveness