PLoS ONE (Jan 2013)

Surveillance and vaccine effectiveness of an influenza epidemic predominated by vaccine-mismatched influenza B/Yamagata-lineage viruses in Taiwan, 2011-12 season.

  • Yi-Chun Lo,
  • Jen-Hsiang Chuang,
  • Hung-Wei Kuo,
  • Wan-Ting Huang,
  • Yu-Fen Hsu,
  • Ming-Tsan Liu,
  • Chang-Hsun Chen,
  • Hui-Hsun Huang,
  • Chi-Hsi Chang,
  • Jih-Haw Chou,
  • Feng-Yee Chang,
  • Tzou-Yien Lin,
  • Wen-Ta Chiu

DOI
https://doi.org/10.1371/journal.pone.0058222
Journal volume & issue
Vol. 8, no. 3
p. e58222

Abstract

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IntroductionThe 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).MethodsInfluenza 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.ResultsDuring 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.ConclusionsThis 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.