(BSPOT01) Variation in the time to complete the primary COVID-19 vaccine series by race, ethnicity, and geography among older US adults

Background: Racial and ethnic disparities exist in COVID-19 vaccination in the United States. However, limited research has investigated racial and ethnic disparities on time to complete the primary (two-dose) vaccine series and the potential impact of geography and social deprivation on disparities.

Objectives: To estimate racial and ethnic differences in the time to complete the primary mRNA vaccine series for COVID-19 among older US Medicare beneficiaries overall and across indicators of rurality and social deprivation.

Methods: We conducted a cross-sectional study using the COVVAXAGE database of CVS and Walgreens customers linked to Medicare claims. We included community-dwelling Medicare beneficiaries who received the first two COVID-19 vaccines between 01/01/2021-12/31/21. The outcome was time between both vaccine doses (categorized as on-time, delayed, or very delayed). We used multinomial logistic regression and model post-estimation commands to generate risk ratios (RR) and 95% confidence intervals (CIs) that described the association between race and ethnicity and timing between vaccine doses. To examine variation in racial and ethnic differences by geography, we used statistical interaction product terms between race and ethnicity, and 1) the six-level National Center for Health Statistics rural-urban scheme and 2) the American Community Survey Social Deprivation Index (SDI).

Results: We identified 11,924,990 Medicare beneficiaries who completed the primary COVID-19 vaccination series (mean age = 75.4 (SD 7.5) years; 60% female; 80% White). Most Medicare beneficiaries completed their primary mRNA vaccine series on time (97.3%). Black (RR=1.30 (95%CI=1.28–1.31)), Hispanic (RR=1.19 (95%CI=1.17–1.20)), and Native American (RR=1.80 (95%CI=1.67–1.94) individuals were more likely to have a delayed second COVID-19 vaccine dose than White individuals, whereas Asian individuals (RR=0.82 (95%CI = 0.80 – 0.84) were less likely to have a delayed second dose. Racial differences in timing varied slightly by urbanicity and social deprivation index (SDI). For example, Black individuals were more likely to have a delayed second dose if they lived in small metro counties (RR=1.41 (95%CI=1.35–1.48)) than if they lived in the most rural counties (RR=1.12 (95%CI=1.05–1.18) when comparing to White individuals in those areas.

Conclusions: Although most Medicare beneficiaries received their second dose of COVID-19 vaccines on time, racial and ethnic differences were found. Relative differences were greatest for Native Americans and those living in living in rural areas. Public health organizations should consider the intersection of sociodemographic characteristics when designing interventions to increase COVID-19 vaccine uptake.