The Impact of Vaccinations on COVID-19 Case Rates at the State Level

Document Type


Publication Date



This study uses a stepwise regression model to measure the efficacy of vaccination in reducing COVID-19 case rates through 8/10/21. In order to hold other covariants constant, variables like density, poverty, and governmental stringency were also included in the regression tests. The statistical results rigorously show that higher vaccination rates led to significantly lower COVID-19 case rates at the state level. A simulation is presented that estimates the cumulative COVID-19 case rate had vaccinations not been available. With respect to the other variables tested, density was significant in positively affecting case rates in 2021 after not being significant in the last half of 2020. Poverty rates were significant during all periods tested in the study. Surprisingly, governmental stringency as measured by the Oxford Stringency Index was not found significant in reducing COVID-19 case rates in 2021. Finally, no significant evidence of herd immunity was found in 2021.


This scholarship is part of the Chapman University COVID-19 Archives.