WHO recognizes that coronavirus can persist in air

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Under increasing pressure from researchers, the World Health Organization acknowledged on Thursday that coronavirus can persist in indoor air and potentially infect people even when they are socially distanced.The UN agency argued that such airborne transmission only occurs during certain medical procedures and that almost all infections occur when people inhale expelled respiratory droplets in their immediate vicinity or when they touch surfaces. contaminated.

But mounting evidence – including “super-spread” events in which several choir singers, restaurants or dance students have been infected – suggests that the virus can be transmitted by microscopic droplets called aerosols, which can float in the air, potentially for hours.

This week, 239 researchers wrote an open letter to WHO, urging officials to accept the possibility that aerosols are a major contributor to the spread of the virus.

In the revised guidelines released Thursday, the WHO recommended avoiding confined spaces with poor ventilation as well as crowded places. But he did not significantly change his position on the masks, arguing that they should only be worn when a social distance of at least six feet is not possible.

The organization said airborne transmission had not been definitively demonstrated, but admitted that it was a possibility in epidemics such as the one that had made 53 of the 61 choir members who had attended a practice sick. March 10 in Washington State. Two of the singers are dead.

“In these events, the transmission of short-range aerosols, especially in specific indoor locations, such as overcrowded and insufficiently ventilated spaces for an extended period with infected people cannot be excluded,” the new guidelines say.

The WHO said more research is “urgently needed to investigate such cases and assess their significance for the transmission of COVID-19”.

Scientists who signed the letter said the new guidelines did not go far enough to take into account the evidence of airborne propagation.

“The WHO slow motion on this issue unfortunately slows down the control of the pandemic,” said Jose Jimenez, chemist at the University of Colorado.

He said that a large part of the public is already ahead of WHO when it comes to masks.

“The masks should be worn indoors, away from the home, at all times, regardless of the distance,” said Jimenez. “Aerosols are more effective in short-range transmission, but they can mix widely in a room and lead to infection, as many cases of super-spread have already shown. ”

At the heart of the scientific debate is the size of the particles that people breathe out and whether these particles fall quickly to the surface or hover in the air. The droplets that humans expel when they cough, sneeze or breathe vary widely and can break into small pieces in the air.

Airborne skeptics say that particles larger than 5 microns are too heavy to travel more than six feet.

But Jimenez said it had been shown by studies as early as 1934. He said that a 50 micron particle could stay in the air for 20 seconds, a 5 micron particle for 15 minutes, and a 1 micron particle. for hours.

“It is shocking to see a large international organization continue to spread this error,” he said.

Donald Milton, an aerosol expert from the University of Maryland, said that “peer-reviewed scientific publications clearly demonstrate that particles, even as large as 30 microns, can travel in air currents and travel more 10 meters indoors ”.

He and other researchers said that the basic concept was well established and that debating the finer points had lost precious time as the coronavirus spread.

For years, scientists have encountered roughly the same resistance regarding influenza, due to the difficulty of capturing samples of the virus from the air, said Milton.

But two research groups have finally proven that the flu is present and the understanding of airborne transmission has become commonplace.

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