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Restricting superspreading events important to slow down spread of coronavirus: Study

Superspreading events are happening more than we expected, more than what could be explained by chance
(Getty Images)
(Getty Images)

Covid-19 is proving to be a tough nut to crack. But studying how the virus behaves can help scientists formulate measures to slow the virus without having to enforce strict lockdowns. A preliminary study suggests one method: stopping superspreading events.

According to the study, the reason coronavirus successfully spreads far and wide are superspreader events. About 20% of Covid-19 cases were responsible for 80% of the local transmission in Hong Kong. The researchers also add that at least 70% of the people did not pass on the disease to others. The study is yet to be tested for errors. 

"That's the picture we have so far," Ben Cowling, from the University of Hong Kong and one of the study co-authors, told Business Insider. "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," he added.

Cowling and his team said their findings could feed into policymaking. Closures targeting high-risk social exposures such as bars, nightclubs, and restaurants could help prevent the occurrence of superspreading events, the team wrote in their study.

What does the study say?

Hong Kong faced two waves of infection, both of which are now contained. The first time, the country quashed the virus due to elaborate testing and tracing. And then, it let its guard down. The country soon had to fight fresh new cases.

The reason coronavirus successfully spreads far and wide are superspreader events. (Getty Images)

Cowling and his team tracked how the new coronavirus moved in the city between January 23 and April 28. Of the 1,038 cases recorded at that time, 349 emerged from its soils. And 196 were linked to just six superspreading events. "One person alone appears to have infected 73 individuals after frequenting several bars in late March. Weddings, temples, hot-pot dinners, work parties, and karaoke venues featured in the other clusters," Dillon C. Adam, from the University of Hong Kong, and Cowling wrote in an opinion that appeared in The New York Times.

Superspreader events

The new coronavirus is not alone in making superspreading events as its hunting grounds. Its closest cousins, SARS and MERS virus, also followed similar patterns.  A 2011 study applies to other infections as well. Researchers found that  20% of a population was responsible for 80% of the transmissions of many diseases, including malaria. They call it the "80-20 rule."

As for Covid-19, a few studies have documented how the virus exploits superspreading events. One study linked about 80% of Covid-19 spread to only 8 to 9% of people in China's Shenzhen. A model proposed by the London School of Hygiene and Tropical Medicine suggested that only 10% of coronavirus cases resulted in  80% of global transmissions.

Scientists have traced several cases back to a superspreading event. For instance, a person who was unaware of their infection at that time passed it on to 53 others during choir practice in Washington.  Another report found that two Covid-19 positive people unwittingly spread the disease to at least 30 people during church gatherings in Arkansas. In South Korea, scientists linked 100 new cases to Zumba classes, adding that the high-intensity workouts may increase the risk of catching and spreading the disease.

Against this backdrop, Cowling and Adam recommend using control tactics that are far less disruptive, socially, and economically.  "Just focus on stopping the superspreading."