title: Effectiveness of the trivalent influenza vaccine in Navarre, Spain, 2010-2011: a population-based test-negative case-control study.
abstract: BACKGROUND
  Some studies have evaluated vaccine effectiveness in preventing outpatient influenza while others have analysed its effectiveness in preventing hospitalizations. This study evaluates the effectiveness of the trivalent influenza vaccine in preventing outpatient illness and hospitalizations from laboratory-confirmed influenza in the 2010-2011 season.
  
  
  METHODS
  We conducted a nested case-control study in the population covered by the general practitioner sentinel network for influenza surveillance in Navarre, Spain. Patients with influenza-like illness in hospitals and primary health care were swabbed for influenza testing. Influenza vaccination status and other covariates were obtained from health care databases. Using logistic regression, the vaccination status of laboratory-confirmed influenza cases was compared with that of test-negative controls, adjusting for age, sex, comorbidity, outpatient visits in the previous 12 months, health care setting, time between symptom onset and swabbing, period and A(H1N1)pdm09 vaccination. Effectiveness was calculated as (1-odds ratio)x100.
  
  
  RESULTS
  The 303 confirmed influenza cases (88% for A(H1N1)pdm09 influenza) were compared with the 286 influenza test-negative controls. The percentage of persons vaccinated against influenza was 4.3% and 15.7%, respectively (p<0.001). The adjusted estimate of effectiveness was 67% (95% CI: 24%, 86%) for all patients and 64% (95% CI: 8%, 86%) in those with an indication for vaccination (persons age 60 or older or with major chronic conditions). Having received both the 2010-2011 seasonal influenza vaccine and the 2009-2010 pandemic influenza vaccine provided 87% protection (95% CI: 30%, 98%) as compared to those not vaccinated.
  
  
  CONCLUSIONS
  The 2010-2011 seasonal influenza vaccine had a moderate protective effect in preventing laboratory-confirmed influenza.
authors.affiliation: Instituto de Salud Pública de Navarra, Leyre 15, 31003, Pamplona, Spain. imartinba@navarra.es
authors.forename: Iván
authors.initials: I
authors.lastname: Martínez-Baz
authors.forename: Víctor
authors.initials: V
authors.lastname: Martínez-Artola
authors.forename: Gabriel
authors.initials: G
authors.lastname: Reina
authors.forename: Marcela
authors.initials: M
authors.lastname: Guevara
authors.forename: Manuel García
authors.initials: MG
authors.lastname: Cenoz
authors.forename: Julio
authors.initials: J
authors.lastname: Morán
authors.forename: Fátima
authors.initials: F
authors.lastname: Irisarri
authors.forename: Maite
authors.initials: M
authors.lastname: Arriazu
authors.forename: Esther
authors.initials: E
authors.lastname: Albeniz
authors.forename: Jesús
authors.initials: J
authors.lastname: Castilla
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D016022:Case-Control Studies; D002648:Child; D002675:Child, Preschool; D015331:Cohort Studies; D057286:Electronic Health Records; D005260:Female; D006760:Hospitalization / Q000706:statistics & numerical data; D006801:Humans; D053118:Influenza A Virus, H1N1 Subtype; D007252:Influenza Vaccines / Q000276:immunology*; D007251:Influenza, Human / Q000453:epidemiology / Q000517:prevention & control*; D008297:Male; D008875:Middle Aged; D018571:Sentinel Surveillance; D013030:Spain / Q000453:epidemiology; D016896:Treatment Outcome; D055815:Young Adult
chemical_list: D007252:Influenza Vaccines