Inequities in COVID-19 vaccine and booster coverage across Massachusetts ZIP codes: large gaps persist after the 2021/22 Omicron wave

Background: Inequities in COVID-19 vaccine coverage may contribute to future disparities in morbidity and mortality between Massachusetts (MA) communities. Methods. We obtained public-use data on residents vaccinated and boosted by ZIP code (and by age group: 5-19, 20-39, 40-64, 65+) from MA Department of Public Health. We constructed population denominators for postal ZIP codes by aggregating Census-tract population estimates from the 2015-2019 American Community Survey. We excluded non-residential ZIP codes and the smallest ZIP codes containing 1% of the state's population. We mapped variation in ZIP-code level primary series vaccine and booster coverage and used regression models to evaluate the association of these measures with ZIP-code-level socioeconomic and demographic characteristics. Because age is strongly associated with COVID-19 severity and vaccine access/uptake, we assessed whether observed socioeconomic and racial inequities persisted after adjusting for age composition and plotted age-specific vaccine and booster coverage by deciles of ZIP-code characteristics. Results. We analyzed data on 418 ZIP codes. We observed wide geographic variation in primary series vaccination and booster rates, with marked inequities by ZIP-code-level education, median household income, essential worker share, and racial-ethnic composition. In age-stratified analyses, primary series vaccine coverage was very high among the elderly. However, we found large inequities in vaccination rates among younger adults and children, and very large inequities in booster rates for all age groups. In multivariable regression models, each 10 percentage point increase in "percent college educated" was associated with a 5.0 percentage point increase in primary series vaccine coverage and a 4.9 percentage point increase in booster coverage. Although ZIP codes with higher "percent Black/Latino/Indigenous" and higher "percent essential workers" had lower vaccine coverage, these associations became strongly positive after adjusting for age and education, consistent with high demand for vaccines among Black/Latino/Indigenous and essential worker populations. Conclusion. One year into MA's vaccine rollout, large disparities in COVID-19 primary series vaccine and booster coverage persist across MA ZIP codes.