Modeling the COVID-19 Vaccination Dynamics in the United States: An Estimation of Coverage Velocity and Carrying Capacity Based on Socio-demographic Vulnerability Indices in California

Bruckhaus, A.; Abedi, A.; Salehi, S.; Pickering, T. A.; Zhang, Y.; Martinez, A.; Lai, M.; Garner, R.; Duncan, D.

Introduction: Coronavirus disease 2019 (COVID-19) disparities among vulnerable populations are a paramount concern that extends to COVID-19 vaccine administration. We aim to better characterize the scope of vaccine inequity in California by comparing the Social Vulnerability Index (SVI) of California counties and respective vaccination rates, modeling the growth rate and anticipated maximum proportion of individuals vaccinated by SVI group. Methods: Overall SVI, its four themes, and 9228 data points of daily vaccination numbers across all 58 California counties were used to model, overall and by theme, growth velocity of proportion of population vaccinated and the expected maximum proportion of individuals (at least 1 dose of Pfizer-BioNTech, Moderna, or Johnson & Johnson/Janssen) that will be vaccinated for each theme. Results: Overall high vulnerability counties in California have lower vaccine coverage velocity compared to low and moderate vulnerability counties. The largest disparity in coverage velocity between low and highly vulnerable counties was observed in Theme 3 (minority status & language). However, our model showed that highly vulnerable counties based on Theme 3 are expected to eventually achieve a higher proportion of vaccinated individuals compared to low vulnerable counterparts if current trajectories continue. Counties in the overall low vulnerability category are estimated to achieve a higher proportion of vaccinated individuals when compared to high and moderate vulnerable counties, assuming current trajectories. The largest disparity in asymptotic proportion vaccinated between high and low vulnerable counties was observed in Theme 2 (household composition & disability). Conclusion: This study provides insight into the problem of COVID-19 vaccine disparity across California which can be used to help promote equity during the current pandemic as well as guide the allocation of future vaccines such as COVID-19 booster shots.