Just 20% of coronavirus cases responsible for 80% of transmissions according to explosive new research

The latest research into so-called “superspreader events” could inform public policy across the world, to help fight the widely feared “second wave” of coronavirus infections, but without the need for strict lockdowns.

A “superspreader” is an infected person who transmits a virus to a large number of people. A growing body of evidence has found that superspreaders account for the vast majority of coronavirus transmissions.  

In the latest study on superspreaders, epidemiologists in Hong Kong analyzed over 1,000 coronavirus cases between January 23 and April 28, and found that just 20 percent of cases were responsible for 80 percent of total transmissions, data which could impact policy around the world. 

About 350 of the cases were community transmissions, while the rest were imported cases. More than 50 percent of the community transmission cases were traced back to just six superspreader events, all of which involved indoor social gatherings that lasted several hours. 

“Superspreading events are happening more than we expected, more than what could be explained by chance. The frequency of superspreading is beyond what we could have imagined,” Ben Cowling, one of the study’s co-authors said.

The study also found that 70 percent of infected people did not pass the virus to anyone else, further highlighting the need for a highly targeted response to defeating the pandemic. 

The work has yet to undergo peer review, but joins a growing body of work indicating the particular method of transmission which has spread the coronavirus to every corner of the globe, with disastrous consequences. If corroborated, however, this research could inform future public policy across the world.  

Among the Hong Kong superspreading events studied, each ‘superspreader’ coronavirus carrier infected three times the average infection rate. The majority of the superspreader cases were traced back to a wedding, an event at a temple, and several bars in Hong Kong's Lan Kwai Fong district.

“You might be wondering if our study, or the experience of Hong Kong, with its small number of total infections, is more broadly representative. We think so,” Cowling wrote, referring to a widely studied phenomenon known as the “80-20 rule” or the “Pareto principle,” in which, for many events, roughly 80 percent of the effects come from 20 percent of the causes. 

Other notable examples of superspreaders: a South Korean churchgoer who infected 43 people in February;  a member of a choir in Washington State who infected some 53 people; and a New York lawyer who infected 100 people in his community. 

Across all of the research which supports the idea that the Pareto principle may be at play in global coronavirus transmission, there is one recurring theme: close, extended indoor contact with superspreaders causes a disproportionate number of infections. 

The key takeaway appears to be that limiting specific types of large gathering could prevent the need for future lockdowns, amid fears of an impending second wave of infection. 

“We’ll be in a much better position to deal with the second wave this fall,” Cowling said. “This knowledge gives us the chance to take more measured actions without going into full lockdown again… Anything outdoors is fine. I'm less concerned about protests,” he added. 

One model from researchers at the London School of Hygiene and Tropical Medicine took it one step further and suggested just 10 percent of coronavirus cases may have accounted for at least 80 percent of transmissions worldwide. Similar results were found in coronavirus research conducted in Israel and China.

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