For social distancing policies that lasted at least 16 to 20 days, the daily rate of infection dropped by more than 9 percentage points, according to the study. Policies lasting 15 days and less also saw declines in the daily infection rate, researchers found. Such social distancing measures, mandated by 95 percent of the country, include shelter-in-place orders, school closures, bans on large events and the closure of gyms, bars and restaurants.

Places with no social distancing orders were at substantially higher risk for infection.

“Holding the amount of voluntary social distancing constant, these results imply 10 times greater spread by April 27 without [shelter-in-place orders] … and more than 35 times greater spread without any of the four measures,” the researchers wrote in “Strong Social Distancing Measures in the United States Reduced the COVID-19 Growth Rate.”