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 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). Conclusion Influenza vaccination before hospitalization was effective in decreasing subsequent mortality and hospital readmission in elderly patients with pneumonia.