Before revision:  A hypothetical national stay-at-home order issued on March 13 , 2020 when a national emergency was declared might have reduced cumulative infections by 63.3\%, and might have helped to reverse exponential growth in the disease by April 10. The results here suggest that a coordinated nationwide stay-at-home order may have reduced by hundreds of thousands the current number of infections and by tens of thousands the total number of deaths from COVID-19.
After revision:  A hypothetical national stay-at-home order issued on March 13 , and a 48.6 percent (31.1 to 61.7) reduction after three weeks. Stay-at-home orders are also associated with a 59.8 percent (18.3 to 80.2) reduction in weekly fatalities after three weeks. These results suggest that stay-at-home order may have reduced by hundreds of thousands the current number of infections and by tens of thousands the total number of deaths from COVID-19.