title: Intradermal and virosomal influenza vaccines for preventing influenza hospitalization in the elderly during the 2011-2012 influenza season: a comparative effectiveness study using the Valencia health care information system.
abstract: BACKGROUND
  The use of intradermal vaccination or virosomal vaccines could increase protection against influenza among the vulnerable population of older adults. Studies assessing the comparative effectiveness of these two influenza vaccine types in this age group are lacking.
  
  
  METHODS
  We conducted a retrospective cohort study to estimate the comparative effectiveness of intradermal seasonal trivalent-influenza vaccine (TIV) delivered by a microneedle injection system and a virosomal-TIV intramuscularly delivered for prevention of influenza hospitalization in non-institutionalized adults aged ≥65 years. We obtained administrative data on immunization status and influenza hospitalization for the 2011-2012 influenza season, and used Cox regression models to assess comparative effectiveness. We estimated crude and adjusted (age, sex, comorbidity, pharmaceutical claims, recent pneumococcal vaccination and number of hospitalizations for all causes other than influenza between the previous and current influenza seasons) hazard ratios (HR).
  
  
  RESULTS
  Overall, 164,021 vaccinated subjects were evaluated. There were 127 hospitalizations for influenza among 62,058 subjects, contributing 914,740 person-weeks at risk in the virosomal-TIV group, and 133 hospitalizations for influenza among 101,963 subjects, contributing 1,504,570 person-weeks at risk in the intradermal-TIV group. The crude HR of intradermal-TIV relative to virosomal-TIV was 0.64 (95% confidence interval (CI): 0.50-0.81), and the adjusted Cox estimated HR was 0.67 (95% CI: 0.52-0.85).
  
  
  CONCLUSIONS
  During the 2011-2012 influenza season the risk of hospitalization for influenza was reduced by 33% in non-institutionalized elderly adults who were vaccinated with intradermal-TIV compared with virosomal-TIV.
authors.affiliation: Área de Investigación en Vacunas, Fundación para el Fomento de la Investigación Sanitaria y Biomédica de la Comunitat Valenciana (FISABIO)-Salud Pública, Valencia, Spain. Electronic address: puig_joa@gva.es.
authors.forename: J
authors.initials: J
authors.lastname: Puig-Barberà
authors.affiliation: Área de Investigación en Vacunas, Fundación para el Fomento de la Investigación Sanitaria y Biomédica de la Comunitat Valenciana (FISABIO)-Salud Pública, Valencia, Spain.
authors.forename: A
authors.initials: A
authors.lastname: Natividad-Sancho
authors.affiliation: Servicio de Análisis de Sistemas de Información Sanitaria, Agencia Valenciana de Salud, Valencia, Spain.
authors.forename: J
authors.initials: J
authors.lastname: Calabuig-Pérez
authors.affiliation: Servicio de Salud Infantil y de la Mujer, Dirección General de Salud Pública, Valencia, Spain.
authors.forename: J A
authors.initials: JA
authors.lastname: Lluch-Rodrigo
authors.affiliation: Servicio de Salud Infantil y de la Mujer, Dirección General de Salud Pública, Valencia, Spain.
authors.forename: E
authors.initials: E
authors.lastname: Pastor-Villalba
authors.affiliation: Área de Investigación en Vacunas, Fundación para el Fomento de la Investigación Sanitaria y Biomédica de la Comunitat Valenciana (FISABIO)-Salud Pública, Valencia, Spain.
authors.forename: S
authors.initials: S
authors.lastname: Martínez-Úbeda
authors.affiliation: Área de Investigación en Vacunas, Fundación para el Fomento de la Investigación Sanitaria y Biomédica de la Comunitat Valenciana (FISABIO)-Salud Pública, Valencia, Spain.
authors.forename: J
authors.initials: J
authors.lastname: Díez-Domingo
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D005260:Female; D006760:Hospitalization / Q000706:statistics & numerical data; D006801:Humans; D007252:Influenza Vaccines / Q000145:classification / Q000627:therapeutic use*; D007251:Influenza, Human / Q000517:prevention & control*; D008297:Male; D016016:Proportional Hazards Models; D012189:Retrospective Studies; D013030:Spain; D022721:Vaccines, Virosome / Q000627:therapeutic use
chemical_list: D007252:Influenza Vaccines; D022721:Vaccines, Virosome
keywords: Aged; Cohort studies; Comparative effectiveness research; Hospitalization; Influenza vaccines