title: Effectiveness of the pandemic H1N1 influenza vaccines against laboratory-confirmed H1N1 infections: population-based case-control study.
abstract: BACKGROUND
  Excellent immune responses following 1 or 2 doses of the monovalent inactivated pandemic H1N1 vaccines have been documented, but the effectiveness of these vaccines against laboratory-confirmed H1N1 infections in the general population is not clear. We evaluated the effectiveness of the pandemic H1N1 and seasonal trivalent influenza vaccines (TIV) used during the 2009 mass vaccination campaign in Manitoba (Canada) in preventing laboratory-confirmed H1N1 infections.
  
  
  METHODS
  A population-based case-control study using data from Cadham Provincial Laboratory (CPL) and the Manitoba Immunization Monitoring System (MIMS). All Manitoba residents ≥6 months of age who had a respiratory specimen tested at CPL for H1N1 were included in the study. Cases were individuals who tested positive for pandemic H1N1 influenza A by reverse transcriptase-PCR (N=1435). Controls were individuals who tested negative for both influenza A and B (N=2309). Information on receipt of TIV or H1N1 vaccine was obtained by record linkage with MIMS, the population-based province-wide immunization registry.
  
  
  RESULTS
  Overall, the adjuvanted H1N1 vaccine was 86% (95%CI 75-93%) effective in preventing laboratory-confirmed H1N1 infections when vaccination occurred ≥14 days before testing. Effectiveness seemed lower among older (≥50 years) individuals [51% (-51 to 84%)] and among those with immunocompromising conditions [67% (-13 to 90%)]. There was also evidence that the H1N1 vaccine might be less effective among those who had received the 2009/10 TIV.
  
  
  CONCLUSIONS
  The adjuvanted H1N1 vaccine used during Manitoba's H1N1 mass vaccination campaign was highly effective against laboratory-confirmed pandemic H1N1 infection, especially among children and younger adults.
authors: Department of Community Health Sciences, University of Manitoba, Winnipeg, Manitoba, Canada. Salah.mahmud@gmail.com
authors: Salaheddin
authors: S
authors: Mahmud
authors: Gregory
authors: G
authors: Hammond
authors: Lawrence
authors: L
authors: Elliott
authors: Tim
authors: T
authors: Hilderman
authors: Carol
authors: C
authors: Kurbis
authors: Patricia
authors: P
authors: Caetano
authors: Paul
authors: P
authors: Van Caeseele
authors: Joel
authors: J
authors: Kettner
authors: Magdy
authors: M
authors: Dawood
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D016022:Case-Control Studies; D002648:Child; D002675:Child, Preschool; D005260:Female; D006801:Humans; D007223:Infant; D053118:Influenza A Virus, H1N1 Subtype / Q000276:immunology / Q000302:isolation & purification*; D007252:Influenza Vaccines / Q000008:administration & dosage / Q000276:immunology*; D007251:Influenza, Human / Q000276:immunology / Q000517:prevention & control* / Q000821:virology*; D008297:Male; D008350:Manitoba; D032541:Mass Vaccination / Q000379:methods; D008875:Middle Aged; D016896:Treatment Outcome; D055815:Young Adult
chemical_list: D007252:Influenza Vaccines