title: Effects of previous influenza vaccination on subsequent readmission and mortality in elderly patients hospitalized with pneumonia.
abstract: OBJECTIVE
  To determine the effect of influenza vaccination on mortality and hospital readmission rates following discharge of elderly patients admitted with pneumonia.
  
  
  METHODS
  We reviewed the medical records of 12,566 randomly selected Medicare beneficiaries hospitalized for pneumonia from October 1 through December 31, 1998, to assess mortality and hospital readmission rates from the date of discharge through the influenza season, May 1, 1999. Patients were grouped based on vaccination status: before hospitalization, during hospitalization, or unknown (no evidence of vaccination).
  
  
  RESULTS
  Severity-adjusted mortality rates were 22.4% (95% confidence interval [CI]: 14.4% to 29.7%) for the vaccination before hospitalization group, 26.4% (95% CI: 20.4% to 31.9%) for the in-hospital vaccination group, and 29.4% (95% CI: 28.1% to 30.6%) for the unknown vaccination status group. Patients vaccinated before hospitalization had significantly lower mortality than did patients with unknown vaccination status (hazard ratio [HR] = 0.65; 95% CI: 0.59 to 0.70; P <0.0001). Adjusted readmission rates were 42.6% (95% CI: 40.0% to 45.1%) for the vaccination before hospitalization group, 40.0% (95% CI: 33.2% to 46.1%) for the in-hospital vaccination group, and 44.8% (95% CI: 43.3% to 46.4%) for the unknown vaccination status group. Patients vaccinated before hospitalization had significantly lower readmission rates than patients with unknown vaccination status (HR = 0.92; 95% CI: 0.87 to 0.98; P = 0.009).
  
  
  CONCLUSIONS
  Influenza vaccination before hospitalization was effective in decreasing subsequent mortality and hospital readmission in elderly patients with pneumonia.
authors.affiliation: Pedicatrics Department, Cedars-Sinai Medical Center, Los Angeles, California 90048, USA. nicole.herzog@cshs.org
authors.forename: Nicole S
authors.initials: NS
authors.lastname: Herzog
authors.forename: Dale W
authors.initials: DW
authors.lastname: Bratzler
authors.forename: Peter M
authors.initials: PM
authors.lastname: Houck
authors.forename: Hui
authors.initials: H
authors.lastname: Jiang
authors.forename: Wato
authors.initials: W
authors.lastname: Nsa
authors.forename: Claudette
authors.initials: C
authors.lastname: Shook
authors.forename: Scott R
authors.initials: SR
authors.lastname: Weingarten
mesh_terms: D000368:Aged; D005260:Female; D006760:Hospitalization / Q000706:statistics & numerical data*; D006801:Humans; D007252:Influenza Vaccines / Q000008:administration & dosage*; D007251:Influenza, Human / Q000517:prevention & control; D008297:Male; D006278:Medicare / Q000706:statistics & numerical data; D010359:Patient Readmission / Q000706:statistics & numerical data*; D011014:Pneumonia / Q000401:mortality* / Q000628:therapy*; D012307:Risk Factors; D016019:Survival Analysis; D014481:United States; D014611:Vaccination
chemical_list: D007252:Influenza Vaccines