Bayesian Inference of State-Level COVID-19 Basic Reproduction Numbers across the United States.

COVID-19 will continue to threaten non-immune persons in the presence of ongoing disease transmission. We can estimate when sustained disease transmission will end by calculating the population-specific basic reproduction number ℛ 0 , which relates to a herd immunity threshold (HIT), given by 1 - 1/ℛ 0 . When the immune fraction of a population exceeds this threshold, sustained disease transmission becomes exponentially unlikely. Here, we report state-level ℛ 0 estimates indicating that disease transmission varies considerably across states. Our ℛ 0 estimates can also be used to determine HITs for the Delta variant of COVID-19. On the basis of Delta-adjusted HITs, vaccination data, and serological survey results, we find that no state has yet achieved herd immunity.