Understanding transmission and intervention for the COVID-19 pandemic in the United States

Li, Yixin; Zhang, Renyi; Zhao, Jiayun; Molina, Mario J.

Abstract The outbreak of the novel coronavirus disease (COVID-19) severely threatens the public health worldwide, but the transmission mechanism and the effectiveness of mitigation measures remain elusive. Here we assess the role of airborne transmission in spreading the disease and the effectiveness of face covering in preventing inter-human transmission in the top-fifteen infected U.S. states during the period between 1 March and 18 May 2020. For all fifteen states, the curve of total confirmed infections exhibits an initial sub-exponential growth and a subsequent linear growth after implementing social distancing/stay-at-home orders. The linearity extends one to two months to the end of our analysis period for the six states without mandated face covering or to the onset of mandated face covering for other nine states with this measure, reflecting a dynamic equilibrium between first-order transmission kinetics and intervention. For the states with mandated face covering, significant deviation from this linearity and curve flattening occur after the onset of this measure for seven states, with exceptions for two states. Most states exhibit persistent upward trends in the daily new infections after social distancing/stay-at-home orders, while downward or slowing trends occur for eight states after implementing mandated face covering. Our results reveal that airborne transmission and face covering play a dominant role in driving the linear growth and curve flattering for the total infections in the U.S., respectively, providing policymakers and the public with compelling evidence for the importance of face covering in fighting the COVID-19 pandemic.