Di I already post this one?
https://www.wsj.com/articles/superspreader-events-offer-clue-on-curbing-coronavirus-11589977873Superspreader Events Offer a Clue on Curbing Coronavirus
Some scientists think banning mass gatherings may be enough to keep the pandemic in check
Some scientists looking for ways to prevent a return to exponential growth in coronavirus infections after lockdowns are lifted are zeroing in on a new approach: focus on avoiding superspreading events.
The theory is that banning mass public events where hundreds of attendees can infect themselves in the space of a few hours, along with other measures such as wearing face masks, might slow the pace of the new coronavirus’s progression to a manageable level even as shops and factories reopen.
Researchers believe that the explosive growth of coronavirus infections that overwhelmed hospitals in some countries was primarily driven by such events earlier this year—horse races in Britain, carnival festivities in the U.S. and Germany or a soccer match in Italy.
The study of superspreading events could help scientists better understand how the virus can propagate in crowded conditions—in offices, schools, churches, gyms and public transportation—and guide governments in regulating such public occasions as weddings, trade conferences and sports games.
There is little doubt about the mechanisms involved in superspreading events. A study published by the National Academy of Sciences in the U.S. last week found that one minute of loud speech was enough to produce thousands of droplets that remain airborne for about 12 minutes, potentially able to infect anyone in the area. Similar studies have shown that virus-laden aerosols, particles smaller than droplets, can levitate for hours after being released in indoors spaces
A more surprising finding is that mass infections tend to be more serious than those contracted in other circumstances, perhaps because of sustained exposure to a larger amount of virus.
Most cases globally, and especially most deaths, happened after superspreading events,” said Hendrik Streeck, a virologist with the University Hospital Bonn, Germany, who published the world-wide first study of a coronavirus superspreading event.
His research into the outbreak in the western county of Heinsberg, which in March became a center of the epidemic in Germany, established that the infection spread across the region like wildfire after around 400 people took part in a traditional carnival party. They drank, sang, kissed and danced for several hours in a large hall on Feb. 15.
The people who attended not only got infected and then spread the virus across the county, but also showed stronger symptoms and a comparatively severe illness, Dr. Streeck says—possibly because they received a higher load of the virus from close and prolonged exposure. Weeks later, thousands were infected across the region and dozens died.
Superspreading events exist in many infectious diseases, but with Covid-19 they are especially dangerous because the virus has a longer period of incubation in which patients show no symptoms but can infect others. Sars and MERS, two other deadly coronaviruses that produced smaller global outbreaks in recent years, were also driven by superspreading events, research has shown
The Mardi Gras festivities in Louisiana, a choir practice in Skagit County, Washington and a meeting of executives of the Biogen drug company near Boston are among the one-off events scientists think helped give the pandemic a fateful boost.
U.S. meatpacking plants, where hundreds have become infected, have also emerged as superspreading sites: counties with or near meatpacking plants have been found to have nearly twice as many Covid-19 cases as the national average, according to an analysis by the Environmental Working Group, a nonprofit organization.
In April, Blaine County in Idaho became one of America’s coronavirus hot spots when hundreds of people tested positive following an apres-ski party. Smaller events like weddings, parties and funerals have also served to turbocharge contagion. In one case, an infected individual visited a funeral and a birthday party within three days in February, spreading the virus to 16 people, three of whom died.
“It is now pretty clear that large groups of people close together are good opportunities to spread the virus,’’ said Marc Lipsitch, professor of epidemiology at the Harvard T.H. Chan School of Public Health.
The experience of several European countries seems to confirm the special role played by superspreading events. Over the past four weeks, Germany, Austria, Denmark, Norway and other countries that have exited early from lockdowns have removed most restrictions on public life except those targeting mass gatherings. So far, new infections have remained low and constant. Sweden, which never had a mandatory lockdown, managed to control and then reduce the spread by relying on only one restrictive measure: prohibiting gatherings of over 50 people.
One remaining question mark regards schools. While no country where schools have reopened has so far reported a sharp increase in infections, some scientists fear schools could act as accelerators for the pandemic.
