Did WHO ignore the risk that new coronavirus floats in air?
Researchers challenge official view of how Covid-19 spreads
Six months into a pandemic that has killed over half a million people, more than 200 scientists from around the world are challenging the official view of how Covid-19 spreads.
The World Health Organisation and the US Centers for Disease Control and Prevention maintain that you have to worry about only two types of transmission: inhaling respiratory droplets from an infected person in your immediate vicinity or less common touching a contaminated surface and then your eyes, nose or mouth.But other experts contend that the guidance ignores growing evidence that a third pathway also plays a significant role in contagion.
How aerosols can hang in air
They say multiple studies demonstrate that particles known as aerosols micro-scopic versions of standard respiratory droplets can hang in the air for long periods and float dozens of feet, making poorly ventilated rooms, buses and other confined spaces dangerous, even when people stay six feet from one another. “We are 100% sure about this,” said Lidia Morawska of Queensland University of Technology in Brisbane. She makes the case in a letter to the WHO accusing it of failing to issue warnings about the risk.
A total of 239 researchers from 32 countries signed the letter, which is set to be published this week in a scientific journal.
Since the coronavirus was first detected in China in December, understanding of how it spreads has evolved considerably, resulting in shifting guidelines regarding the use of masks.
At first, the World Health Organisation (WHO) and the US Centres for Disease Control and Prevention (CDC) said masks were overkill for ordinary people and should be conserved for health workers. Later, the CDC recommended masks only for people with Covid-19 symptoms.
In April, after it became clear that people without symptoms could also spread the virus, the CDC suggested masks for everybody when physical distancing was difficult, a position the WHO eventually adopted.
Advantages
The proponents of aerosol transmission said masks worn correctly would help prevent the escape of exhaled aerosols as well as inhalation of the microscopic particles. But they said the spread could also be reduced by improving ventilation and zapping indoor air with ultraviolet light in ceiling units.
Jose Jimenez, a University of Colorado chemist who signed the letter, said the idea of aerosol transmission should not frighten people. “It’s not like the virus has changed,” he said.
“We think the virus has been transmitted this way all along.”
He and other scientists cited several studies supporting the idea that aerosol transmission is a serious threat.
As early as mid-March, a study in the New England Journal of Medicine found that when the virus was suspended in mist under laboratory conditions it remained “viable and infectious” for three hours, which researchers said equated to as much as half an hour in realworld conditions.
It had already been established that some people, known as “super spreaders,” happen to be especially good at exhaling fine material, producing 1,000 times more than others. A recent study found coronavirus RNA in hallways near hospital rooms of Covid-19 patients. Another
raised concerns that aerosols laden with the virus were shed by floor-cleaning equipment and by health workers removing personal protective gear.
It was the outbreak among choir members in Mount Vernon,
Washington, and a report about the incident in The Times that first piqued the interest of several of the aerosol proponents. Of 61 singers at a March 10 rehearsal, all but eight became sick. Two people died.
A team led by Shelly Miller, a University of Colorado professor, dug into church-hall blueprints, furnace specifications, locations of choir members and hours of attendance. The researchers diagrammed movements of the singer who was identified as the person who brought the virus to practice.
Donald Milton, a University of Maryland professor, said the average person breathes 10,000 litres of air each day. “You only need one infectious dose of the coronavirus in 10,000 litres,” he said.