ORIGINAL INVESTIGATION

Benefits of Influenza Vaccination for Low-, Intermediate-, and High-Risk Senior Citizens
Kristin L. Nichol, MD, MPH; J. Wuorenma, RN, BSN; T. von Sternberg, MD

Background: Vaccination rates for healthy senior citizens are lower than those for senior citizens with underlying medical conditions such as chronic heart or lung disease. Uncertainty about the benefits of influenza vaccination for healthy senior citizens may contribute to lower rates of utilization in this group. Objective: To clarify the benefits of influenza vaccina-

tion among low-risk senior citizens while concurrently assessing the benefits for intermediate- and high-risk senior citizens.
Methods: All elderly members of a large health maintenance organization were included in each of 6 consecutive study cohorts. Subjects were grouped according to risk status: high risk (having heart or lung disease), intermediate risk (having diabetes, renal disease, stroke and/or dementia, or rheumatologic disease), and low risk. Outcomes were compared between vaccinated and unvaccinated subjects after controlling for baseline demographic and health characteristics. Results: There were more than 20 000 subjects in each

pitalizations (P .001), a 32% decrease in hospitalizations for all respiratory conditions (P .001), and a 27% decrease in hospitalizations for congestive heart failure (P .001). Immunization was also associated with a 50% reduction in all-cause mortality (P .001). Within the risk subgroups, vaccine effectiveness was 29%, 32%, and 49% for high-, intermediate-, and low-risk senior citizens for reducing hospitalizations for pneumonia and influenza (for high and low risk, P .002; for intermediate risk, P = .11). Effectiveness was 19%, 39%, and 33% (for each, P .008), respectively, for reducing hospitalizations for all respiratory conditions and 49%, 64%, and 55% for