All states in the U.S. initiated social distancing measures between March 10 and March 25, 2020. Researchers predicted that this type of intervention will prevent a rapid, overwhelming epidemic according to modeling studies. Governments also enacted physical distancing measures in prior pandemics including the 1918 influenza pandemic with moderate success.
Prior to the coronavirus pandemic, there wasn’t much evidence about the net benefits of imposing statewide social distancing measures to reduce the transmission of viral infections. Because of this, a team of researchers from the United States, South Africa, and the United Kingdom conducted a study on it. They wanted to know what the COVID-19 case growth rate was, before and after social distancing measures where enacted. And, what the public health impacts of government-mandated non-pharmacological interventions were after they started and before they ended.
A search of government websites and third-party sources provided nationwide social distancing measures implemented between January 21 and May 1, 2020. These sources included the New York Times COVID-19 database from which they obtained daily state-specific reported COVID-19 cases and deaths. The measures included cancellations of public events, restrictions on internal movement, and closures of schools, workplaces, and state borders. Researchers also sought for state orders to shelter-in-place, also referred to as lockdowns, and categorized them as restrictions on internal movement.
What researchers found was:
- Beginning 4 days after social distancing, the case growth rate declined by ~ 1% per day.
- Beginning 7 days after social distancing, the mortality growth rate decreased by 2% per day.
However, they did not observe a major difference in the average daily case growth rate, before versus after, statewide restrictions on internal movement were enacted. Though separating their close connection with one another did prove difficult.
The authors’ findings imply that social distancing reduced the total number of COVID-19 cases substantially every week:
- 1st week by approximately 1,600.
- 2nd week by approximately 55,000
- 3rd week by approximately 600,000