title: Case-Control Study of Vaccine Effectiveness in Preventing Laboratory-Confirmed Influenza Hospitalizations in Older Adults, United States, 2010-2011.
abstract: BACKGROUND
  Older adults are at increased risk of influenza-associated complications, including hospitalization, but influenza vaccine effectiveness (VE) data are limited for this population. We conducted a case-control study to estimate VE to prevent laboratory-confirmed influenza hospitalizations among adults aged ≥50 years in 11 US Emerging Infections Program hospitalization surveillance sites.
  
  
  METHODS
  Cases were influenza infections (confirmed by reverse-transcription polymerase chain reaction) in adults aged ≥50 years hospitalized during the 2010-2011 influenza season, identified through Emerging Infections Program surveillance. Community controls, identified through home telephone lists, were matched by age group (±5 years), county, and month of hospitalization for case patients. Vaccination status was determined by self-report (with location and date) or medical records. Conditional logistic regression models were used to calculate adjusted VE (aVE) estimates (100 × [1 - adjusted odds ratio]), adjusting for sex, race, socioeconomic factors, smoking, chronic medical conditions, recent hospitalization for a respiratory condition, and functional status.
  
  
  RESULTS
  Among case patients, 205 of 368 (55%) were vaccinated, compared with 489 of 773 controls (63%). Case patients were more likely to be of nonwhite race and more likely to have ≥2 chronic health conditions, a recent hospitalization for a respiratory condition, an income <$35 000, and a lower functional status score (P < .01 for all). The aVE was 56.8% (95% confidence interval, 34.1%-71.7%) and was similar across age groups, including adults ≥75 years (aVE, 57.3%; 15.9%-78.4%).
  
  
  CONCLUSIONS
  During 2010-2011, influenza vaccination was associated with a significant reduction in the risk of laboratory-confirmed influenza hospitalization among adults aged ≥50 years, regardless of age group.
authors.affiliation: Influenza Division, Centers for Disease Control and Prevention.
authors.forename: Fiona
authors.initials: F
authors.lastname: Havers
authors.affiliation: Influenza Division, Centers for Disease Control and Prevention.|Battelle Memorial Institute.
authors.forename: Leslie
authors.initials: L
authors.lastname: Sokolow
authors.affiliation: Influenza Division, Centers for Disease Control and Prevention.
authors.forename: David K
authors.initials: DK
authors.lastname: Shay
authors.affiliation: Emory University School of Medicine.|VA Medical Center, Atlanta, Georgia.
authors.forename: Monica M
authors.initials: MM
authors.lastname: Farley
authors.affiliation: Maryland Department of Health and Mental Hygiene, Baltimore.
authors.forename: Maya
authors.initials: M
authors.lastname: Monroe
authors.affiliation: Connecticut Emerging Infections Program, Yale School of Public Health, New Haven.
authors.forename: James
authors.initials: J
authors.lastname: Meek
authors.affiliation: California Emerging Infections Program, Oakland.
authors.forename: Pam
authors.initials: P
authors.lastname: Daily Kirley
authors.affiliation: University of Rochester School of Medicine and Dentistry, New York.
authors.forename: Nancy M
authors.initials: NM
authors.lastname: Bennett
authors.affiliation: Minnesota Department of Health, St Paul.
authors.forename: Craig
authors.initials: C
authors.lastname: Morin
authors.affiliation: Colorado Department of Public Health and Environment, Denver.
authors.forename: Deborah
authors.initials: D
authors.lastname: Aragon
authors.affiliation: Oregon Public Health Division, Portland.
authors.forename: Ann
authors.initials: A
authors.lastname: Thomas
authors.affiliation: Vanderbilt University School of Medicine, Nashville, Tennessee.
authors.forename: William
authors.initials: W
authors.lastname: Schaffner
authors.affiliation: New York State Department of Health, Albany.
authors.forename: Shelley M
authors.initials: SM
authors.lastname: Zansky
authors.affiliation: New Mexico Department of Health, Santa Fe.
authors.forename: Joan
authors.initials: J
authors.lastname: Baumbach
authors.affiliation: Influenza Division, Centers for Disease Control and Prevention.
authors.forename: Jill
authors.initials: J
authors.lastname: Ferdinands
authors.affiliation: Influenza Division, Centers for Disease Control and Prevention.
authors.forename: Alicia M
authors.initials: AM
authors.lastname: Fry
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D016022:Case-Control Studies; D005260:Female; D006760:Hospitalization / Q000706:statistics & numerical data*; D006801:Humans; D007114:Immunization / Q000706:statistics & numerical data*; D007252:Influenza Vaccines; D007251:Influenza, Human / Q000453:epidemiology* / Q000517:prevention & control*; D008297:Male; D008875:Middle Aged; D014481:United States / Q000453:epidemiology
chemical_list: D007252:Influenza Vaccines
keywords: influenza vaccination; influenza vaccine effectiveness; influenza-associated hospitalization; older adults