Policy and weather influences on mobility during the early U.S. COVID-19 pandemic

Abstract As the novel coronavirus severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) 24 continues to proliferate across the globe, it is a struggle to predict and prevent its spread. The 25 successes of mobility interventions demonstrate how policies can help limit the person-to-person 26 interactions that are essential to infection. With significant community spread, experts predict this 27 virus will continue to be a threat until safe and effective vaccines have been developed and 28 widely deployed. We aim to understand mobility changes during the first major quarantine period 29 in the United States, measured via mobile device tracking, by assessing how people changed their 30 behavior in response to policies and to weather. Here, we show that consistent national messaging 31 was associated with consistent national behavioral change, regardless of local policy. 32 Furthermore, although human behavior did vary with outdoor air temperature, these variations 33 were not associated with variations in a proxy for the rate of encounters between people. The 34 independence of encounters and temperatures suggests that weather-related behavioral changes 35 will, in many cases, be of limited relevance for SARS-CoV-2 transmission dynamics. Both of 36 these results are encouraging for the potential of clear national messaging to help contain any 37 future pandemics, and possibly to help contain COVID-19.Published in PNAS: https://www.pnas.org/content/118/22/e2018185118