title: Effectiveness of neuraminidase inhibitors in preventing hospitalization during the H1N1 influenza pandemic in British Columbia, Canada.
abstract: OBJECTIVE
  In British Columbia (BC), Canada, neuraminidase inhibitors (NIs) were publicly funded during the 2009 A(H1N1)pdm09 pandemic for treatment of high-risk patients and/or anyone with moderate-to-severe illness. We assessed antiviral effectiveness (AVE) against hospitalization in that context.
  
  
  METHODS
  A population-based cohort study was conducted using linked administrative data. The cohort included all individuals living in BC during the study period (1 September to 31 December 2009) with a diagnostic code consistent with influenza or pandemic H1N1. The main study period pertained to the second-wave A(H1N1)pdm09 circulation (1 October to 31 December 2009), with sensitivity analyses around the more specific pandemic peak (18 October to 7 November). Exposure was defined by same-day NI prescription. The main outcome was all-cause hospitalization within 14 days of the outpatient influenza diagnosis. Cox proportional hazards models assessed AVE with 1 : 1 propensity-score matching and covariate adjustment.
  
  
  RESULTS
  After matching, there were 304/58,061 NI-exposed and 345/58,061 unexposed patients hospitalized during the main study period. The very young [<6 months (35.0; 95% CI 16.7-73.4)], the old [65-79 years (13.7; 95% CI 10.1-18.6)] and the very old [≥80 years (38.7; 95% CI 26.6-56.5)] had the highest hospitalization rate per 1000 patients overall. Fully adjusted AVE against all-cause hospitalization during the main study period was 16% (95% CI 2%-28%), similar to the pandemic peak (15%; 95% CI -4%-30%).
  
  
  CONCLUSIONS
  The use of NIs was associated with modest protection against hospitalization during the 2009 pandemic, but appeared underutilized in affected age groups with the highest hospitalization risk.
authors.affiliation: University of British Columbia, Vancouver, BC, Canada.
authors.forename: Fawziah
authors.initials: F
authors.lastname: Marra
authors.forename: Mei
authors.initials: M
authors.lastname: Chong
authors.forename: Bonnie
authors.initials: B
authors.lastname: Henry
authors.forename: David M
authors.initials: DM
authors.lastname: Patrick
authors.forename: Perry
authors.initials: P
authors.lastname: Kendall
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000998:Antiviral Agents / Q000627:therapeutic use*; D001955:British Columbia; D002648:Child; D002675:Child, Preschool; D015331:Cohort Studies; D005260:Female; D006760:Hospitalization / Q000706:statistics & numerical data*; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D053118:Influenza A Virus, H1N1 Subtype / Q000187:drug effects*; D007251:Influenza, Human / Q000188:drug therapy*; D008297:Male; D008875:Middle Aged; D009439:Neuraminidase / Q000037:antagonists & inhibitors*; D053139:Oseltamivir / Q000627:therapeutic use; D012189:Retrospective Studies; D016896:Treatment Outcome; D055815:Young Adult; D053243:Zanamivir / Q000627:therapeutic use
chemical_list: D000998:Antiviral Agents; D053139:Oseltamivir; D009439:Neuraminidase; D053243:Zanamivir
keywords: antivirals; cohort; mortality; oseltamivir; population-based; zanamivir