title: Mid-Season Estimates of Influenza Vaccine Effectiveness against Influenza A(H3N2) Hospitalization in the Elderly in Quebec, Canada, January 2015.
abstract: BACKGROUND
  The 2014/15 influenza season in Canada was characterized by an early epidemic due to vaccine-mismatched influenza A(H3N2) viruses, disproportionately affecting elderly individuals ≥65-years-old. We assessed vaccine effectiveness (VE) against A(H3N2) hospitalization among elderly individuals during the peak weeks of the 2014/15 epidemic in Quebec, Canada.
  
  
  METHODS
  Nasal specimens and clinical/epidemiological data were collected within 7 days of illness onset from elderly patients admitted with respiratory symptoms to one of four participating hospitals between November 30, 2014 and January 13, 2015. Cases tested RT-PCR positive for influenza A(H3N2) and controls tested negative for any influenza. VE was assessed by test-negative case-control design.
  
  
  RESULTS
  There were 314 participants including 186 cases (62% vaccinated) and 128 controls (59% vaccinated) included in primary VE analysis. Median age was 81.5 years, two-thirds were admitted from the community and 91% had underlying comorbidity. Crude VE against A(H3N2) hospitalization was -17% (95%CI: -86% to 26%), decreasing to -23% (95%CI: -99 to 23%) with adjustment for age and comorbidity, and to -39% (95%CI: -142 to 20%) with additional adjustment for specimen collection interval, calendar time, type of residence and hospital. In sensitivity analyses, VE estimates were improved toward the null with restriction to participants admitted from the community (-2%; 95%CI: -105 to 49%) or with specimen collection ≤4 days since illness onset (- 8%; 95%CI: -104 to 43%) but further from the null with restriction to participants with comorbidity (-51%; 95%CI: -169 to 15%).
  
  
  CONCLUSIONS
  The 2014/15 mismatched influenza vaccine provided elderly patients with no cross-protection against hospitalization with the A(H3N2) epidemic strain, reinforcing the need for adjunct protective measures among high-risk individuals and improved vaccine options.
authors.affiliation: Biological, Environmental and Occupational Risks, Institut National de Santé Publique du Québec, Quebec, QC, Canada; CHU de Quebec, Quebec, QC, Canada; Laval University, Quebec, QC, Canada.
authors.forename: Rodica
authors.initials: R
authors.lastname: Gilca
authors.affiliation: Influenza & Emerging Respiratory Pathogens, British Columbia Centre for Disease Control, Vancouver, British Columbia, Canada.
authors.forename: Danuta M
authors.initials: DM
authors.lastname: Skowronski
authors.affiliation: Biological, Environmental and Occupational Risks, Institut National de Santé Publique du Québec, Quebec, QC, Canada.
authors.forename: Monique
authors.initials: M
authors.lastname: Douville-Fradet
authors.affiliation: Biological, Environmental and Occupational Risks, Institut National de Santé Publique du Québec, Quebec, QC, Canada.
authors.forename: Rachid
authors.initials: R
authors.lastname: Amini
authors.affiliation: Biological, Environmental and Occupational Risks, Institut National de Santé Publique du Québec, Quebec, QC, Canada; CHU de Quebec, Quebec, QC, Canada.
authors.forename: Nicole
authors.initials: N
authors.lastname: Boulianne
authors.affiliation: Bureau de surveillance et de vigie, Ministère de la Santé et des Services sociaux du Québec, Quebec, QC, Canada.
authors.forename: Isabelle
authors.initials: I
authors.lastname: Rouleau
authors.affiliation: Laboratoire de santé publique du Québec, Institut National de Santé Publique du Québec, Montreal, Canada.
authors.forename: Christine
authors.initials: C
authors.lastname: Martineau
authors.affiliation: Laboratoire de santé publique du Québec, Institut National de Santé Publique du Québec, Montreal, Canada.
authors.forename: Hugues
authors.initials: H
authors.lastname: Charest
authors.affiliation: Biological, Environmental and Occupational Risks, Institut National de Santé Publique du Québec, Quebec, QC, Canada; CHU de Quebec, Quebec, QC, Canada; Laval University, Quebec, QC, Canada.
authors.forename: Gaston
authors.initials: G
authors.lastname: De Serres
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D005260:Female; D006760:Hospitalization / Q000706:statistics & numerical data; D006801:Humans; D053122:Influenza A Virus, H3N2 Subtype / Q000235:genetics* / Q000276:immunology*; D007252:Influenza Vaccines / Q000627:therapeutic use*; D007251:Influenza, Human / Q000276:immunology / Q000517:prevention & control* / Q000821:virology*; D008297:Male; D009666:Nose / Q000821:virology; D011792:Quebec / Q000453:epidemiology; D018571:Sentinel Surveillance
chemical_list: D007252:Influenza Vaccines