Researchers Answer Why Rapidly Expanding Social Distancing Measures are Crucial

Wednesday, March 18, 2020 - 11:40

Based on a new study in China, mild cases of COVID-19 that go unrecognized are fueling the coronavirus pandemic.

According to the Science News report, researchers used data on people’s movement in China from January 10 to January 23 to simulate how COVID-19 spread before restrictions on travel within the country and other isolation measures were implemented.

Undocumented cases — those occurring in people with mild or no symptoms — accounted for an estimated 86 percent of all infections, the team reports online March 16 in Science.

Those undetected cases were less infectious — 55 percent as infectious, the simulation found — than the known cases. But with high numbers on their side, the hidden cases became the source for almost 80 percent of the diagnosed infections.

“It’s the undocumented cases that are driving the spread and growth of the outbreak,” Jeffrey Shaman, an infectious disease researcher at Columbia University, said March 16 at a news briefing.

Shaman and his colleagues simulated the spread of the coronavirus with data that estimated the movement of people between 375 cities in China. The study focused on the time leading up to the Chinese New Year in late January, a period when people were traveling more and the virus moved through society relatively unimpeded before the concerted response effort.

The researchers also considered the impact of measures taken after January 23, including travel restrictions between Wuhan and other Chinese cities, self-quarantine recommendations and the increasing availability of testing.

With social distancing efforts to limit the spread of undetected cases, and more testing to identify who was sick and isolate them, the tide turned: Documented cases accounted for the majority — 65 percent — of infections.


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