Study: Many Americans started staying home well before COVID-19 mandates, slowing infection rates

BALTIMORE — From Manhattan to Los Angeles, many Americans saw the writing on the wall regarding  the coronavirus from the start. According to a new study from Johns Hopkins University, residents of the 25 U.S. counties hit the hardest by COVID-19 started limiting their movements long before (6-29 days) official state mandates were issued. Despite those areas still suffering extraordinary rates of the disease, it might have been far worse if not for those vigilant citizens.

Using mobile phone location data to track locals’ daily movements in these counties, researchers highlight a noteworthy level of social distancing. Those preemptive decisions to stay home more often than usual did indeed the spread of COVID-19 in the beginning stages of the pandemic, the authors say.

Counties hit hardest by COVID-19
A social distancing ratio of 0 indicates no trips. A value of 0.5 indicates half the number of trips relative to baseline. 1 indicates no change in behavior. Lower ratios indicate residents of that county stayed home more than others. (Courtesy: Johns Hopkins University)

“Our results strongly support the conclusion that social distancing played a crucial role in the reduction of case growth rates in multiple U.S. counties during March and April, and is therefore an effective mitigation policy for COVID-19 in the United States,” says research leader Lauren Gardner, co-director of the Center for Systems Science and Engineering at Johns Hopkins, in a release.

“Critically, if individual-level actions were not taken and social distancing behavior was delayed until the state-level directives were implemented, COVID-19 would have been able to circulate unmitigated for additional weeks in some locations, inevitably resulting in more infections and deaths,” Gardner adds. “This demonstrates that it is within the power of each U.S. resident to help slow the spread of COVID-19.”

Social distancing before social distancing

While there were a few county mandates issued to limit movements before official state announcements, 21 out of the 25 examined counties saw drops in local movement before rules were put into place.


To start, the research team needed to formulate a piece of baseline data for normal movement activity in a given area. For that purpose, they focused on local movements in examined counties between January 8th and January 31st, long before COVID-19 was a relevant consideration for Americans. Then, they tracked any fluctuations in those movement rates through April 16th.

Compared to January 8th through 23rd, people in the 25 hardest hit counties traveled and moved around far less often between January 24th and April 17th. People really started staying home more often beginning in early March, which was long before California issued the first state directive to stay home on March 21st.

Take New York City for example; by early March NYC residents were moving around only 35% as much as they had been in January. NYC had the largest reduction in local movements of all 25 examined areas. Conversely, Harris County in Texas (which includes the city of Houston) saw the smallest reduction in movements. Locals in Harris County were traveling in March about 65% as much as they had in January.

Small sacrifices goes long way in curbing COVID-19 spread

All in all, the study’s authors say their findings vindicate social distancing and lockdowns as valid ways to curb the spread of COVID-19.

“Individuals seem to have anticipated public health directives in March and April, despite a mixed political message,” Hamada Badr, a co-author and research scientist in the Department of Earth and Planetary Sciences at Johns Hopkins, explains. “As stay-at-home policies began to relax, we urge individuals and governments to make safe and data-driven decisions, to respond to the potential risk of increased infections. More timely, consistent and decisive policy implementation of social distancing and other known effective mitigation measures is urgently needed.”

The study is published in Lancet Infectious Diseases. 

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