COVID-19 vaccine uptake in United States counties: geospatial vaccination patterns and trajectories towards herd immunity

Following the COVID-19 pandemic, safe and effective vaccines were developed and authorized for use in the general population. Studying factors that encourage community acceptance of these vaccines is needed to prevent proliferation of SARS-CoV-2 variants, to safely relax local restrictions, and to return to pre-pandemic living conditions. To our knowledge, United States (US) county-level disparities in vaccination are yet to be investigated. Our data span February - May 2021 across 3138 US counties. We consider percentage of residents with at least one dose of an authorized COVID vaccine as the outcome. Spatio-temporal models were used to determine associations of vaccination rates with time-fixed and time-varying covariates. Spatial variability was modelled via Conditional Auto-regressive models; county trajectories over time were specified using random slopes. Greater vaccination rates occur in counties with older residents, high educational attainment, and high proportion of minority residents. Vaccination rates change with COVID risk metrics, suggesting continued slowing of vaccine uptake due to decreasing incidence and infection rates. County effects reveal strong regional patterns in average vaccination rates and trajectories. Although local herd immunity can be expected in August 2021 for counties with typical uptake rates, these counties are clustered in relatively few areas of the country.