Impact of influenza immunization on medical expenditures among Medicare elderly, 1999-2003.

Background: The impact of influenza immunization on expenditures for inpatient, outpatient, and professional services among elderly Medicare beneficiaries between 1999 and 2003 was examined.

Methods: Data were from independent annual survey samples of 175,000 beneficiaries. Response rates ranged from 64% to 71%. Survey data included beneficiaries' demographics, education, supplemental insurance, perceived health, and influenza vaccination. Baseline measures, derived from Medicare claims for the year prior to influenza season, included service utilization, comorbidities, influenza immunization, and health status. The outcome measure was medical expenditures for acute and chronic respiratory conditions (ACRCs) for each 33-week annual influenza season.

Results: Total expenditures for ACRCs were lower among the immunized population during all four seasons. The amount and statistical significance of the savings varied with the severity of the virus and the vaccine match to the prevalent influenza strains. During the 1999-2000 influenza season, which had the most severe virus and a close vaccine match, average costs for ACRCs were $88 lower among immunized beneficiaries than among nonimmunized beneficiaries (equivalent to a 3.06% savings). During the 2002-2003 season, which had a less severe virus but the highest vaccine match rate, average costs for ACRCs were $103 lower for immunized beneficiaries than for nonvaccinated beneficiaries (equivalent to a 3.12% savings). The relative reduction in ACRC expenditures among vaccinated beneficiaries is attributable to less frequent use of inpatient services.

Conclusions: In addition to improving the health of older Americans, meeting the Healthy People 2010 influenza immunization goal of 90% among the elderly should also result in lower Medicare expenditures.