title: Surveillance and vaccine effectiveness of an influenza epidemic predominated by vaccine-mismatched influenza B/Yamagata-lineage viruses in Taiwan, 2011-12 season.
abstract: BACKGROUND
  The 2011-12 trivalent influenza vaccine contains a strain of influenza B/Victoria-lineage viruses. Despite free provision of influenza vaccine among target populations, an epidemic predominated by influenza B/Yamagata-lineage viruses occurred during the 2011-12 season in Taiwan. We characterized this vaccine-mismatched epidemic and estimated influenza vaccine effectiveness (VE).
  
  
  METHODS
  Influenza activity was monitored through sentinel viral surveillance, emergency department (ED) and outpatient influenza-like illness (ILI) syndromic surveillance, and case-based surveillance of influenza with complications and deaths. VE against laboratory-confirmed influenza was evaluated through a case-control study on ILI patients enrolled into sentinel viral surveillance. Logistic regression was used to estimate VE adjusted for confounding factors.
  
  
  RESULTS
  During July 2011-June 2012, influenza B accounted for 2,382 (72.5%) of 3,285 influenza-positive respiratory specimens. Of 329 influenza B viral isolates with antigen characterization, 287 (87.2%) were B/Yamagata-lineage viruses. Proportions of ED and outpatient visits being ILI-related increased from November 2011 to January 2012. Of 1,704 confirmed cases of influenza with complications, including 154 (9.0%) deaths, influenza B accounted for 1,034 (60.7%) of the confirmed cases and 103 (66.9%) of the deaths. Reporting rates of confirmed influenza with complications and deaths were 73.5 and 6.6 per 1,000,000, respectively, highest among those aged ≥65 years, 50-64 years, 3-6 years, and 0-2 years. Adjusted VE was -31% (95% CI: -80, 4) against all influenza, 54% (95% CI: 3, 78) against influenza A, and -66% (95% CI: -132, -18) against influenza B.
  
  
  CONCLUSIONS
  This influenza epidemic in Taiwan was predominated by B/Yamagata-lineage viruses unprotected by the 2011-12 trivalent vaccine. The morbidity and mortality of this vaccine-mismatched epidemic warrants careful consideration of introducing a quadrivalent influenza vaccine that includes strains of both B lineages.
authors.affiliation: Centers for Disease Control, Taipei, Taiwan, Republic of China.
authors.forename: Yi-Chun
authors.initials: YC
authors.lastname: Lo
authors.forename: Jen-Hsiang
authors.initials: JH
authors.lastname: Chuang
authors.forename: Hung-Wei
authors.initials: HW
authors.lastname: Kuo
authors.forename: Wan-Ting
authors.initials: WT
authors.lastname: Huang
authors.forename: Yu-Fen
authors.initials: YF
authors.lastname: Hsu
authors.forename: Ming-Tsan
authors.initials: MT
authors.lastname: Liu
authors.forename: Chang-Hsun
authors.initials: CH
authors.lastname: Chen
authors.forename: Hui-Hsun
authors.initials: HH
authors.lastname: Huang
authors.forename: Chi-Hsi
authors.initials: CH
authors.lastname: Chang
authors.forename: Jih-Haw
authors.initials: JH
authors.lastname: Chou
authors.forename: Feng-Yee
authors.initials: FY
authors.lastname: Chang
authors.forename: Tzou-Yien
authors.initials: TY
authors.lastname: Lin
authors.forename: Wen-Ta
authors.initials: WT
authors.lastname: Chiu
mesh_terms: D000293:Adolescent; D000328:Adult; D016022:Case-Control Studies; D002648:Child; D002675:Child, Preschool; D058872:Epidemics; D005260:Female; D006801:Humans; D007223:Infant; D007252:Influenza Vaccines / Q000627:therapeutic use*; D007251:Influenza, Human / Q000453:epidemiology* / Q000517:prevention & control*; D008297:Male; D008875:Middle Aged; D010045:Outpatients; D012044:Regression Analysis; D018571:Sentinel Surveillance; D013624:Taiwan / Q000453:epidemiology; D013997:Time Factors; D055815:Young Adult
chemical_list: D007252:Influenza Vaccines