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

At a particular moment in time, the total number of COVID-19 infections depends on the growth rate of infections on all prior days. Thus, persistent decreases in growth rates have a compounding effect on total infections, at least until a shrinking susceptible population slows growth through a different mechanism. To provide a sense of scale and context for our main results in Figures 2 and 3, we integrate the growth rate of infections in each locality from Figure 3 to estimate total infections to date, both with actual anti-contagion policies and in the "no policy" counterfactual scenario. To account for the declining size of the susceptible population in each administrative unit, we couple our econometric estimates for the effects of policies to a simple Susceptible-Infected-Removed (SIR) model of infectious disease dynamics 7, 22 (see Methods). This allows us to extend our projections beyond the initial exponential growth phase of infections, a threshold which our results suggest would currently be exceeded in several countries in the "no policy" scenario.