BENEFITS OF INFLUENZA VACCINATION FOR LOW-RISK, INTERMEDIATE-RISK, AND HIGH-RISK SENIOR-CITIZENS

Background: Vaccination rates for healthy senior citizens are lower th an those for senior citizens with underlying medical conditions such a s chronic heart or lung disease. Uncertainty about the benefits of inf luenza vaccination for healthy senior citizens may contribute to lower rates of utilization in this group. Objective: To clarify the benefit s of influenza vaccination among low-risk senior citizens while concur rently assessing the benefits for intermediate- and high-risk senior c itizens. Methods: All elderly members of a large health maintenance or ganization were included in each of 6 consecutive study cohorts. Subje cts were grouped according to risk status: high risk (having heart or lung disease), intermediate risk (having diabetes, renal disease, stro ke and/or dementia, or rheumatologic disease), and low risk. Outcomes were compared between vaccinated and unvaccinated subjects after contr olling for baseline demographic and health characteristics. Results: T here were more than 20 000 subjects in each of the 6 cohorts who provi ded 147 551 person-periods of observation. The pooled vaccination rate was 60%. There were 101 619 person-periods of observation for low-ris k subjects, 15 482 for intermediate-risk, and 30 450 for highrisk subj ects. Vaccination over the 6 seasons was associated with an overall re duction of 39% for pneumonia hospitalizations (P < .001), a 32% decrea se in hospitalizations for all respiratory conditions (P < .001), and a 21% decrease in hospitalizations for congestive heart failure (P < . 001). Immunization was also associated with a 50% reduction in all-cau se mortality (P < .001). Within the risk subgroups, vaccine effectiven ess was 29%, 32% and 49% for high-, intermediate-, and low-risk senior citizens for reducing hospitalizations for pneumonia and influenza (f or high and low risk, P less than or equal to .002; for intermediate r isk, P = .11). Effectiveness was 19%, 39%, and 33% (for each, P less t han or equal to .008), respectively, for reducing hospitalizations for all respiratory conditions and 49%, 64%, and 55% for reducing deaths from all causes (for each, P < .001). Vaccination was also associated with direct medical care cost savings of $73 per individual vaccinated for all subjects combined (P = .002). Estimates of cost savings withi n each risk group suggest that vaccination would be cost saving for ea ch subgroup (range of cost savings of $171 per individual vaccinated f or high risk to $7 for low risk), although within the subgroups these findings did not reach statistical significance (for each, P greater t han or equal to .05). Conclusions: This study confirms that healthy se nior citizens as well as senior citizens with underlying medical condi tions are at risk for the serious complications of influenza and benef it from vaccination. All individuals 65 years or older should be immun ized with this vaccine.