KEYWORDS:
Influenza
Adult Immunization
Outcomes
Hospitalization

BACKGROUND:
Although the benefits of influenza immunization have been clearly described for community-dwelling elderly patients, the impact of prior vaccination on outcomes for patients who are hospitalized is unknown.

OBJECTIVE(S):
To determine if prior immunization would reduce the subsequent rate of mortality and readmission following hospital discharge of elderly patients with pneumonia.

METHOD(S):
As a part of the Medicare National Pneumonia Project, we evaluated the medical records of 12,565 patients, aged 65 years or greater, discharged from the hospital between October 1 and December 31, 1998, with a diagnosis of pneumonia. Immunization status was determined for patients in the cohort using a combination of chart review and Medicare Part B immunization claims data. Unique patient identifiers were linked to Medicare claims data and the denominator file to identify those patients who were readmitted to the hospital or who died prior to May 1, 1999. All outcomes were risk-adjusted.

RESULT(S):
Patients who were immunized prior to hospitalization had a reduced mortality rate (Hazard Ratio [HR] 0.65, 95% CI 0.59-0.70, p<0.0001) as compared to those patients with unknown immunization status. Similarly, patients in the Prior/In-hospital group had a reduced mortality rate (HR 0.70, 95% CI 0.65-0.76, p<0.0001) as compared to those in the unknown group. When hospital readmission was the outcome of interest, patients who were immunized prior to their stay had a lower rate of subsequent hospitalization (HR 0.92, 95% CI 0.87-0.98, p=0.009) than those patients for whom immunization status was unknown.

CONCLUSIONS(S):
Influenza immunization administered prior to hospitalization was associated with a reduction in subsequent mortality and admission for elderly patients with pneumonia.

LEARNING OBJECTIVES:
1. Understand the risk of subsequent hospitalization for influenza or influenza-related illness in hospitalized patients.
2. Understand the benefits of influenza immunization to reduce mortality and subsequent hospitalization in hospitalized elderly patients with pneumonia.