"The measures we’ve put in place appear to be working," said Dr. Jeffrey Duchin, the head of King County's health department, on a conference call with journalists this afternoon.
"We are looking at reductions in person-to-person contact that have progressively improved and have led us to a point where we believe that we’re making a very positive impact on the course of this epidemic," Duchin said.
He warned, however, that it will be "months" before people in this region can think about getting back to something resembling the old "normal," and he promised that if people here let up on social distancing efforts too soon, "the outbreak will come roaring back, big time."
Duchin bases this outlook, in part, on a study by the Institute for Disease Modeling that used aggregated Facebook data (available through that company's "Data for Good" effort) to suggest that people in the Seattle area have dramatically altered their regular movements since a series of tightening social distancing guidelines began being announced in early March.
Seattleites are staying put in residentially zoned areas, the data show, and are staying away from business districts and the University of Washington's campus.
A second report from IDM uses computational modeling to suggest that given this apparently decreased social interaction, and given many other assumptions, the rate of transmission in the Seattle area has likely decreased, with each person who has COVID-19 no longer infecting 2.7 new people but instead 1.4 new people.
That roughly 50 percent decrease in the estimated rate of new infections is not enough to cause the overall spread of the epidemic to go down in Seattle. For that to happen, the number of new infections generated by each new COVID-19 case needs to drop below 1.
But it's progress.
Duchin said he can't at this point predict when a "peak" in local infections will arrive.
Washington state as a whole is now nearing 5,000 known infections and nearly 200 deaths, the vast majority of them in King County. However, hospitals are not yet overwhelmed—a sign that the work to increase healthcare bed capacity and encourage public social distancing to limit new infections is paying off.
Duchin stressed repeatedly that today's relatively positive news "in no way" means that it's time to relax social distancing. For example, the IDM study of Facebook location data found "fluctuating adherence" on weekends—perhaps as people stop working at home and head for local parks. And, in any case, the new rate of transmission suggested by the other IDM study isn't yet good enough to point the local infection curve downward.
Even if we get past a "peak" in Seattle area infections, Duchin said, many other conditions probably need to be in place before social distancing rules can be relaxed.
Among them: extremely widespread availability of testing with rapid turnaround times, dramatic enhancements to local health systems, and the ability of our currently overtaxed public health agencies to isolate newly infected individuals and then quickly trace their contacts.