Coronavirus: Reports Find Social Distancing Works, Must Continue

SEATTLE, WA — A pair of new reports from the Bellevue-based Institute for Disease Modeling shows promising results for social distancing efforts in Washington, but researchers say it is essential those measures continue to succeed in limiting the peak of the coronavirus outbreak.

The IDM released the reports Monday, examining the effectiveness of current policies to limit the virus's spread in King County and the Seattle metro. Researchers analyzed information from state and county health departments, and anonymized mobility data from Facebook to compare transmission rates against decreasing public movements.

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From Seattle and King County Public Health:

"The IDM researchers then looked to see if these reductions in mobility could be related to reductions in COVID-19 transmission. Using a simulation of COVID-19 testing, diagnosis and death data for King County, they found that a measure of transmission, called the effective reproductive number, dropped by about half from about 2.7 in late February to roughly 1.4 on March 18th. This number represents the number of new transmissions stemming from each infection. In order to sustain a drop in new cases, each infected person, on average, must infect fewer than one person."

Researchers said the information provided from Facebook was collected from mobile users with location services enabled and does not identify individuals. Using that data, the report compared "mobility patterns" for roughly 230,000 people between Feb. 26 and March 28, finding a nearly 90 percent reduction in overall movement during daytime and nighttime hours by March 28.

Visits to commercial areas, the report finds, have steadily dropped as each social distancing policy was implemented, while the concentration of people remaining in residential areas has generally increased.

The report noted an uptick in mobility during the weekends, but researchers said that number may also reflect increased grocery shopping trips and outdoor exercise.

"We are seeing a positive effect from the social distancing and other measures we've put in place, although significant numbers of cases and deaths continue to occur," said. Dr. Jeff Duchin, health officer for King County. "It's important to note that these findings are based on relatively few cases and persons testing, and therefore come with a great deal of uncertainty."

As of Sunday night, nearly 4,900 COVID-19 cases were confirmed in Washington, and 195 people have died. King County accounts for 2,161 of the state's illnesses and 144 of the deaths associated with the virus.

"No one should take these findings as an indication to relax our social distancing strategy," Duchin said. "The threat of a rebound that could overwhelm the healthcare system remains and will remain for the foreseeable future if we let up too soon."

During a conference call with reporters Monday afternoon, Duchin said it would likely take weeks to get a fuller understanding of the rate of transmission, and even longer before the state can consider rolling back protective measures.

"I don't see that in the next month," Duchin said.

According to Duchin, Washington is still likely months away from returning to normal activities, but there could be an opportunity to "moderate our approach" sooner if there is sufficient evidence that doing so would not cause further harm.

"It would be very much a mistake to interpret these results as a reason to let up," Duchin said.