Differences in COVID-19 XBB.1.5 vaccination coverage: A decomposition analysis across racial and ethnic groups in a...

Differences in COVID-19 vaccination coverage across racial and ethnic groups have been widely documented in the U.S. We conducted Blinder-Oaxaca decomposition analyses to examine the contribution of 13 risk factors to COVID-19 XBB.1.5 vaccination differences across racial and ethnic groups within a large U.S. healthcare system.

The retrospective cohort included adult members of Kaiser Permanente Southern California between September 12, 2023, and April 30, 2024. The outcome was COVID-19 XBB.1.5 vaccination. We used multivariable logistic regression to assess the association of demographic factors, socioeconomic status measured by neighborhood deprivation index (NDI), clinical factors, and healthcare utilization with vaccination. Decomposition analyses were performed to quantify the extent to which differences in these factors explained differences in vaccination rates between Hispanic, non-Hispanic Black, and non-Hispanic White individuals.

Among 2,621,148 members eligible for decomposition analyses, COVID-19 XBB.1.5 vaccination rates were 25.5%, 15.5% and 19.7% for non-Hispanic White, Hispanic, and non-Hispanic Black individuals, respectively. Decomposition analyses showed that 78.9% of the vaccination difference between Hispanic and non-Hispanic White individuals and 86.2% of the difference between non-Hispanic Black and non-Hispanic White individuals were explained by observed risk factors. With non-Hispanic White individuals serving as the reference group, differences in age distribution explained 22.3% of the difference for Hispanic individuals and 11.5% for non-Hispanic Black individuals, and NDI explained 12.0% and 21.2%, respectively; differences in prior season influenza vaccination and prior bivalent COVID-19 vaccination accounted for 10.5% and 29.3% of the difference for Hispanic individuals, and 30.8% and 19.3% for non-Hispanic Black individuals, respectively. When prior vaccination history was excluded, the share of the difference explained by age and NDI increased substantially.

Differences in COVID-19 XBB.1.5 vaccination across race/ethnicity were largely explained by differences in age, socioeconomic status, and healthcare utilization. The findings underscore the need for targeted interventions, particularly in younger populations and highly deprived neighborhoods, as well as leveraging outpatient visits to improve vaccine uptake.