County Social Vulnerability and Influenza Vaccine Rates: National and Local Estimates for Medicare Recipients

Introduction: Seasonal influenza vaccination among older adults is well below the recommendation of Healthy People 2020. Although geographic disparities in influenza vaccination are well documented, it remains unclear how community attributes correlate with influenza vaccination rates. Social vulnerability measures play an important role in interventions addressing vaccine equity; however, social vulnerability dimensions as corollaries of vaccination are poorly understood. To inform vaccine equity interventions, this analysis investigates spatially varying associations between county social vulnerability and influenza vaccination rate among Medicare recipients. Methods: County-level 2018 data (N=3,105) from the Centers for Disease Control and Prevention's Social Vulnerability Index were merged with the percentage of Medicare recipients vaccinated against influenza. Multilevel linear regression and geographically weighted regression generated global and local estimates, adjusted for potential confounders. Analyses were conducted in November 2020–April 2021. Results: A 10-percentile point increase in the overall Social Vulnerability Index was associated with an 0.87-point decrease in percentage vaccinated (p<0.001) with substantial variation by Social Vulnerability Index theme and geography. A 10-percentile point increase in socioeconomic vulnerability was associated with a 1.6-point decrease in vaccination (p<0.001) with stronger associations in higher Social Vulnerability Index quartiles and in parts of the Midwest, South, and coastal Northeast. Other Social Vulnerability Index themes had smaller associations with mixed directions: household composition and disability estimates were negative, whereas estimates for minority status and language and housing and transportation were positive. Conclusions: Medicare recipients in socioeconomically vulnerable counties have low influenza vaccination rates, particularly in select regions of the country. Best practices to improve vaccine access and uptake should be targeted and should explicitly consider local socioeconomic vulnerability.