Social distancing strategies for curbing the COVID-19 epidemic

Stephen M Kissler; Christine Tedijanto; Marc Lipsitch; Yonatan Grad

We used the open critical care capacity of the United States, 0.89 free beds per 10,000 adults, as a benchmark for critical care demand (2) . We simulated epidemic trajectories based on an epidemic establishment time of 11 March 2020. We simulated social distancing by reducing R0 by a fixed proportion, which ranged between 0 and 60%, on par with the reduction in R0 achieved in China through intense social distancing measures (3) . We assessed 'one-time' social distancing interventions, for which R0 was reduced by up to 60% for a fixed duration of time (up to 20 weeks) starting two weeks after epidemic establishment. We also assessed intermittent social distancing measures, for which social distancing was turned 'on' when the prevalence of infection rose above a threshold and 'off' when it fell below a second, lower threshold, with the goal of keeping the number of critical care patients below 0.89 per 10,000 adults. An 'on' threshold of 37.5 cases per 10,000 people achieved this goal in both the seasonal and non-seasonal cases with wintertime R0 = 2. We chose 10 cases per 10,000 adults as the 'off' threshold. We performed a sensitivity analysis around these threshold values (Figures S2-S3 ) to assess how they affected the duration and frequency of the interventions. Finally, we assessed the impact of doubling critical care capacity (and the associated on/off thresholds) on the frequency and overall duration of the period social distancing measures.