The Effect of Large-Scale Anti-Contagion Policies on the Coronavirus (COVID-19) Pandemic

Solomon Hsiang; Daniel Allen; Sebastien Annan-Phan; Kendon Bell; Ian Bolliger; Trinetta Chong; Hannah Druckenmiller; Andrew Hultgren; Luna Yue Huang; Emma Krasovich; Peiley Lau; Jaecheol Lee; Esther Rolf; Jeanette Tseng; Tiffany Wu

Here we directly estimate the effects of local, regional, and national policies on the growth rate of infections across localities within China, South Korea, Iran, Italy, France, and the US (see Figure 1 and Appendix Table A1 ). We compile publicly available sub-national data on daily infection rates and the timing of policy deployments, including (1) travel restrictions, (2) social distancing through cancellation of events and suspensions of educational/commercial/religious activities, (3) quarantines and lockdowns, and (4) additional policies such as emergency declarations or expansions of paid sick leave, from the earliest available dates to the present (March 18, 2020; see complete descriptions in the Appendix). Because the pandemic is still in its early stages, populations in these countries remain almost entirely susceptible to COVID-19, causing the natural spread of infections 3 to exhibit almost perfect exponential growth. 7, 14, 22 The rate of this exponential growth may change daily and is determined by epidemiological factors, such as disease infectivity and contact networks, as well as policies that induce behavior changes. 7, 8, 22 We cannot experimentally manipulate policies ourselves, but because they are being deployed while the epidemic unfolds, we can measure their impact empirically. We examine how the growth rate of infections each day in a given locality changes in response to the collection of ongoing policies applied to that locality on that day.