title: Detailed Report on 2014/15 Influenza Virus Characteristics, and Estimates on Influenza Virus Vaccine Effectiveness from Austria's Sentinel Physician Surveillance Network.
abstract: BACKGROUND
  Influenza vaccine effectiveness (VE) is influenced by the antigenic similarity between vaccine- and circulating strains.
  
  
  METHODS
  This paper presents data obtained by the Austrian sentinel surveillance system on the evolution of influenza viruses during the season 2014/15 and its impact on influenza vaccine effectiveness in primary care in Austria as estimated by a test-negative case control design. VE estimates were performed for each influenza virus type/subtype, stratified by underlying diseases and adjusted for age, sex and calendar week of infection.
  
  
  RESULTS
  Detailed genetic and antigenic analyses showed that circulating A(H3N2) viruses were genetically distinct from the 2014/15 A(H3N2) vaccine component indicating a profound vaccine mismatch. The Influenza A(H1N1)pdm09 viruses were antigenically conserved and matched the respective vaccine component. Influenza B viruses were lineage-matched B/Yamagata viruses with a clade-level variation. Consistent with substantial vaccine mismatch for the A(H3N2) viruses a crude overall VE of only 47% was estimated, whereas the VE estimates for A(H1N1)pdm09 were 84% and for influenza B viruses 70%. Increased VE estimates were obtained after stratification by underlying diseases and adjustment for the covariates sex and age, whereby the adjustment for the calendar week of infection was the covariate exerting the highest influence on adjusted VE estimates.
  
  
  CONCLUSIONS
  In summary, VE data obtained in this study underscore the importance to perform VE estimates in the context of detailed characterization of the contributing viruses and also demonstrate that the calendar week of influenza virus infection is the most important confounder of VE estimates.
authors.affiliation: Department of Virology, Medical University Vienna, Vienna, Austria.
authors.forename: Monika
authors.initials: M
authors.lastname: Redlberger-Fritz
authors.affiliation: Institute of Environmental Health, Center for Public Health, Medical University Vienna, Vienna, Austria.
authors.forename: Michael
authors.initials: M
authors.lastname: Kundi
authors.affiliation: Department of Virology, Medical University Vienna, Vienna, Austria.
authors.forename: Theresia
authors.initials: T
authors.lastname: Popow-Kraupp
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D001317:Austria; D005260:Female; D006801:Humans; D053118:Influenza A Virus, H1N1 Subtype; D053122:Influenza A Virus, H3N2 Subtype; D007252:Influenza Vaccines / Q000008:administration & dosage*; D007251:Influenza, Human / Q000453:epidemiology*; D008297:Male; D011320:Primary Health Care; D018571:Sentinel Surveillance
chemical_list: D007252:Influenza Vaccines