  The emergence of SARS-CoV-2 and the coronavirus infectious disease (COVID-19)
has become a pandemic. Social (physical) distancing is a key non-pharmacologic
control measure to reduce the transmission rate of SARS-COV-2, but high-level
adherence is needed. Using daily travel distance and stay-at-home time derived
from large-scale anonymous mobile phone location data provided by Descartes
Labs and SafeGraph, we quantify the degree to which social distancing mandates
have been followed in the U.S. and its effect on growth of COVID-19 cases. The
correlation between the COVID-19 growth rate and travel distance decay rate and
dwell time at home change rate was -0.586 (95% CI: -0.742 ~ -0.370) and 0.526
(95% CI: 0.293 ~ 0.700), respectively. Increases in state-specific doubling
time of total cases ranged from 1.04 ~ 6.86 days to 3.66 ~ 30.29 days after
social distancing orders were put in place, consistent with mechanistic
epidemic prediction models. Social distancing mandates reduce the spread of
COVID-19 when they are followed.
