A new study found that social distancing worked to limit the spread of coronavirus in the United States and may have prevented tens of millions of infections.
The study, published Thursday in the journal Health Affairs, found that government-imposed social distancing cut the virus’ daily growth rate by about 9% after roughly three weeks.
Without any social distancing measures at all, the number of coronavirus cases in the US could have been 35 times higher, the researchers estimated.
The report’s abstract, says that state and local governments imposed social distancing measures in March and April of 2020 to contain the spread of novel coronavirus disease 2019 (COVID-19). These included large event bans, school closures, closures of entertainment venues, gyms, bars, and restaurant dining areas, and shelter-in-place orders (SIPOs). We evaluated the impact of these measures on the growth rate of confirmed COVID-19 cases across US counties between March 1, 2020 and April 27, 2020. An event-study design allowed each policy’s impact on COVID-19 case growth to evolve over time. Adoption of government-imposed social distancing measures reduced the daily growth rate by 5.4 percentage points after 1–5 days, 6.8 after 6–10 days, 8.2 after 11–15 days, and 9.1 after 16–20 days. Holding the amount of voluntary social distancing constant, these results imply 10 times greater spread by April 27 without SIPOs (10 million cases) and more than 35 times greater spread without any of the four measures (35 million). Our paper illustrates the potential danger of exponential spread in the absence of interventions, providing relevant information to strategies for restarting economic activity.
CNN reports “Our paper illustrates the potential danger of exponential spread in the absence of interventions, providing relevant information to strategies for restarting economic activity,” they wrote. Charles Courtemanche from the University of Kentucky — as well and colleagues there and at the University of Louisville and Georgia State University – estimated the effects of social distancing by comparing coronavirus cases in counties with and without a number of social distancing measures.
Shelter-in-place orders and the closure of restaurants and bars seemed particularly effective at slowing the spread of the virus, the researchers found. Bans on large events and the closure of public schools alone didn’t seem to affect the growth rate.
“[Our] results argue against returning to partial measures such as school closures and restrictions on large gatherings, while removing the restrictions that prevent the redirection of social activity to other settings,” the researchers wrote.
They did note that their study had some limitations. Official case counts, for example, are likely an undercount because they may not include people who aren’t sick enough to go to the doctor.
Other factors could have skewed the results too, such as “informal encouragement by government officials to wear masks or improve hygiene, changing business practices, and social norms regarding distancing.”
CNN / Health Affairs Journal