Effects of previous influenza vaccination on subsequent readmission and mortality in elderly patients hospitalized with pneumonia

PURPOSE: 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 I 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% Cl: 20.4% to 31.9%) for the in-hospital vaccination group, and 29.4% (95% Cl: 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% Cl: 40.0% to 45.1%) for the vaccination before hospitalization group, 40.0% (95% Cl: 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% Cl: 0.87 to 0.98; P = 0.009). CONCLUSION: Influenza vaccination before hospitalization was effective in decreasing subsequent mortality and hospital readmission in elderly patients with pneumonia. (C) 2003 by Excerpta Medica Inc.