“The gain with the lockdown was probably not that big in itself,” Kim Sneppen, professor of biocomplexity at Copenhagen University, told The Local. “It was this gain indirectly by reducing situations where these people meet many other people. Avoiding large gatherings helps to keep the infection down.”
Together with Lone Simonsen, professor of population health sciences at Roskilde University, Sneppen assumed that ten percent of the population were responsible for 80 percent of coronavirus infections, as some recent international studies have suggested, and then applied this idea to the Danish data.
They found that such a model much better explained why the rate of spread in Denmark had continued to decrease after the lifting of lockdown restrictions from mid-April.
The new study, published on the preprint server medRxiv, concludes as a result that a relatively small number of so-called superspreaders probably played the key role in spreading coronavirus around Danish society.
Sneppen said that he and Simonsen had felt the need to make a new model after their existing model failed to explain why Denmark's reproduction number — the number of people on average each infected person infects — had stayed so low despite the reopening of schools and lifting of other restrictions.
Sneppen said that the superspreader theory also much better explained the case of Sweden, where the reproduction number has fallen below 1 without many hard restrictions ever being put in place.
“Our explanation is that Sweden has banned larger gatherings and events, that people have limited their diversity of social contacts, and thus prevented the superspreaders from spreading the infection,” Sneppen said.
Sneppen said he had no idea why superspreaders seemed to infect more people than average.
“I think it is just people who produce more virus, they are not dirty in any way, they are just unlucky to have the virus somewhere where it is going out in the air to meet other people,” he added.
He said that the study's findings suggested that banning big events rather than closing schools should be top of the list of countermeasures if there is a second wave.
“It's not only big events, you would need to ban whatever activities make a superspreader a superspreader, so any situation where you meet a lot of different people during a day, you should reduce that,” he said.
“If you are a travelling salesman and are very active you could do a lot of damage,” he said. “Sitting in a crowded bus is probably not a good idea. I would have people put on face masks there.”
“I would also recommend that people can be sociable, they can talk with different friends every day, but they should not talk with too many different friends in one day, because then they could be a superspreader.”
The two researchers' theory is a pre-print which has not been peer-reviewed.
But if it turns out to be right, Sneppen said Sweden's higher death toll might turn out to be mainly a result of its delay in banning large gatherings. “They put a ban on big events, but it was some time later than Denmark,” he said,