title: Effectiveness of the 2010-2011 seasonal influenza vaccine in preventing confirmed influenza hospitalizations in adults: a case-case comparison, case-control study.
abstract: BACKGROUND
  We estimated influenza vaccine effectiveness (IVE) to prevent laboratory-confirmed influenza-related hospitalizations in patients 18 years old or older during the 2010-2011 influenza season.
  
  
  METHODS
  We conducted a prospective case-control study in five hospitals, in Valencia, Spain. Study subjects were consecutive emergency hospitalizations for predefined conditions associated with an influenza-like illness episode <8 days before admission. Patients were considered immunized if vaccinated ≥14 days before influenza-like illness onset. Cases were those with a real time reverse transcriptase polymerase chain reaction (RT-PCR) positive for influenza and controls were RT-PCR positive for other respiratory viruses. Adjusted IVE was estimated as 100×(1-adjusted odds ratio). To account for indication bias we computed adjusted IVE for respiratory syncytial virus related hospitalizations.
  
  
  RESULTS
  Of 826 eligible hospitalized patients, 102 (12%) were influenza positive and considered cases, and 116 (14%) were positive for other respiratory viruses and considered controls. Adjusted IVE was 54% (95% confidence interval, 11-76%). By subgroup, adjusted IVE was 53% (4-77%) for those with high-risk conditions, 59% (16-79%) for those ≥60 years of age, and, 54% (4-79%) for those ≥60 years of age with high-risk conditions. No influenza vaccine effect was observed against respiratory syncytial virus related hospitalization.
  
  
  CONCLUSIONS
  Influenza vaccination was associated with a significant reduction on the risk of confirmed influenza hospitalization, irrespective of age and high-risk conditions.
authors: Centro Superior de Investigación en Salud Pública CSISP, Valencia, Spain. puig joa@gva.es
authors: J
authors: J
authors: Puig-Barberà
authors: J
authors: J
authors: Díez-Domingo
authors: A
authors: A
authors: Arnedo-Pena
authors: M
authors: M
authors: Ruiz-García
authors: S
authors: S
authors: Pérez-Vilar
authors: J L
authors: JL
authors: Micó-Esparza
authors: A
authors: A
authors: Belenguer-Varea
authors: C
authors: C
authors: Carratalá-Munuera
authors: V
authors: V
authors: Gil-Guillén
authors: H
authors: H
authors: Schwarz-Chavarri
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D016022:Case-Control Studies; D005260:Female; D006760:Hospitalization / Q000706:statistics & numerical data*; D006801:Humans; D007252:Influenza Vaccines; D007251:Influenza, Human / Q000453:epidemiology / Q000517:prevention & control*; D008297:Male; D008875:Middle Aged; D011446:Prospective Studies; D012307:Risk Factors; D013030:Spain / Q000453:epidemiology; D014611:Vaccination / Q000706:statistics & numerical data; D055815:Young Adult
chemical_list: D007252:Influenza Vaccines