Variation in the time to complete the primary COVID-19 vaccine series by race, ethnicity, and geography among older US adults

Introduction: Racial and ethnic disparities in COVID-19 vaccine access are well-documented; however, few studies have examined whether racial disparities are modified by other factors, including geographic location and arealevel deprivation. Methods: We conducted an observational study using the COVVAXAGE database. Medicare beneficiaries who received the COVID-19 vaccine primary series (two doses) between 01/01/2021 and 12/31/2021 were included. Racial differences in the time between doses was assessed by urbanicity using g-formula methods. Results: We identified 11,924,990 beneficiaries (mean age = 75.4; 60% female; 80% White). Most beneficiaries (97.1 %) received their second vaccine on time. Delayed second doses were more common among beneficiaries who were Black (RRdelayed = 1.30, 95 %CI = 1.28-1.31) and rural (RRdelayed = 1.27, 95 %CI = 1.25-1.29) relative to White and urban beneficiaries. Racial disparities in delayed vaccinations varied in magnitude by degree of urbanicity. Conclusions: Most beneficiaries received their second COVID-19 vaccine on time. Racial disparities were observed and shown to vary by geographic area.