title: Does Influenza Vaccination Modify Influenza Severity? Data on Older Adults Hospitalized With Influenza During the 2012-2013 Season in the United States.
abstract: BACKGROUND
  Some studies suggest that influenza vaccination might be protective against severe influenza outcomes in vaccinated persons who become infected. We used data from a large surveillance network to further investigate the effect of influenza vaccination on influenza severity in adults aged ≥50 years who were hospitalized with laboratory-confirmed influenza.
  
  
  METHODS
  We analyzed influenza vaccination and influenza severity using Influenza Hospitalization Surveillance Network (FluSurv-NET) data for the 2012-2013 influenza season. Intensive care unit (ICU) admission, death, diagnosis of pneumonia, and hospital and ICU lengths of stay served as measures of disease severity. Data were analyzed by multivariable logistic regression, parametric survival models, and propensity score matching (PSM).
  
  
  RESULTS
  Overall, no differences in severity were observed in the multivariable logistic regression model. Using PSM, adults aged 50-64 years (but not other age groups) who were vaccinated against influenza had a shorter length of ICU stay than those who were unvaccinated (hazard ratio for discharge, 1.84; 95% confidence interval, 1.12-3.01).
  
  
  CONCLUSIONS
  Our findings show a modest effect of influenza vaccination on disease severity. Analysis of data from seasons with different predominant strains and higher estimates of vaccine effectiveness are needed.
authors.affiliation: Epidemic Intelligence Service Program Influenza Division, Centers for Disease Control and Prevention.
authors.forename: Carmen S
authors.initials: CS
authors.lastname: Arriola
authors.affiliation: Department of Medicine, Emory University School of Medicine Atlanta Veterans Affairs Medical Center, Georgia.
authors.forename: Evan J
authors.initials: EJ
authors.lastname: Anderson
authors.affiliation: New Mexico Department of Health, Santa Fe.
authors.forename: Joan
authors.initials: J
authors.lastname: Baumbach
authors.affiliation: Department of Medicine, University of Rochester School of Medicine and Dentistry.
authors.forename: Nancy
authors.initials: N
authors.lastname: Bennett
authors.affiliation: Michigan Department of Community Health, Lansing.
authors.forename: Susan
authors.initials: S
authors.lastname: Bohm
authors.affiliation: Salt Lake County Health Department, Utah.
authors.forename: Mary
authors.initials: M
authors.lastname: Hill
authors.affiliation: Vanderbilt University School of Medicine, Nashville, Tennessee.
authors.forename: Mary Lou
authors.initials: ML
authors.lastname: Lindegren
authors.affiliation: Ohio Department of Health, Columbus.
authors.forename: Krista
authors.initials: K
authors.lastname: Lung
authors.affiliation: Connecticut Emerging Infections Program, Yale School of Public Health, New Haven.
authors.forename: James
authors.initials: J
authors.lastname: Meek
authors.affiliation: Rhode Island Department of Health, Providence.
authors.forename: Elizabeth
authors.initials: E
authors.lastname: Mermel
authors.affiliation: Colorado Department of Public Health and Environment, Denver.
authors.forename: Lisa
authors.initials: L
authors.lastname: Miller
authors.affiliation: Maryland Department of Health and Mental Hygiene, Baltimore.
authors.forename: Maya L
authors.initials: ML
authors.lastname: Monroe
authors.affiliation: Minnesota Department of Health, St. Paul.
authors.forename: Craig
authors.initials: C
authors.lastname: Morin
authors.affiliation: Iowa Department of Public Health, Des Moines.
authors.forename: Oluwakemi
authors.initials: O
authors.lastname: Oni
authors.affiliation: California Emerging Infections Program, Oakland.
authors.forename: Arthur
authors.initials: A
authors.lastname: Reingold
authors.affiliation: Vanderbilt University School of Medicine, Nashville, Tennessee.
authors.forename: William
authors.initials: W
authors.lastname: Schaffner
authors.affiliation: Oregon Public Health Division, Portland.
authors.forename: Ann
authors.initials: A
authors.lastname: Thomas
authors.affiliation: Emerging Infections Program, New York State Department of Health, Albany, New York.
authors.forename: Shelley M
authors.initials: SM
authors.lastname: Zansky
authors.affiliation: Influenza Division, Centers for Disease Control and Prevention.
authors.forename: Lyn
authors.initials: L
authors.lastname: Finelli
authors.affiliation: Influenza Division, Centers for Disease Control and Prevention.
authors.forename: Sandra S
authors.initials: SS
authors.lastname: Chaves
mesh_terms: D000368:Aged; D005260:Female; D006760:Hospitalization; D006801:Humans; D007252:Influenza Vaccines / Q000276:immunology*; D007251:Influenza, Human / Q000276:immunology* / Q000401:mortality / Q000517:prevention & control; D007362:Intensive Care Units; D016015:Logistic Models; D008297:Male; D008875:Middle Aged; D011014:Pneumonia / Q000175:diagnosis*; D012621:Seasons; D012720:Severity of Illness Index; D014481:United States; D014611:Vaccination
chemical_list: D007252:Influenza Vaccines
keywords: adults; influenza; influenza vaccine; severe illness
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