SEATTLE – Six months after a pandemic that has killed more than half a million people, more than 200 researchers from around the world are challenging the official idea of how the coronavirus is spreading.
The World Health Organization and the US Centers for Disease Control and Prevention claim that you only have to worry about two types of transmission: inhaling respiratory drops from an infected person in your immediate vicinity or ̵
But other experts argue that the guidance ignores growing evidence that a third path plays an important role.
They say that several studies show particles known as aerosols – microscopic versions of common 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 live 6 meters from eachother.
“We are 100% sure of this,” said Lidia Morawska, professor of atmospheric science and environmental engineering at Queensland University of Technology in Brisbane, Australia.
She does this in an open letter to the WHO accusing the UN agency of failing to provide appropriate warnings. A total of 239 researchers from 32 countries signed the letter, which will be published next week in a scientific journal.
In interviews, experts said aerosol transmission seems to be the only way to explain several “super-spreading” events, including infection of diners at a restaurant in China that sat at separate tables and by chorus members in Washington state who took precautions during a rehearsal.
WHO officials have acknowledged that the virus can be transmitted through aerosols but say it only occurs during medical procedures such as intubation that can germinate large amounts of the microscopic particles. CDC officials did not respond to several requests for comment.
Dr. Benedetta Allegranzi, one of the WHO’s best experts on infection prevention and control, said in response to questions from The Times that Morawska and her group presented theories based on laboratory experiments rather than field evidence.
“We value and respect their views and contributions to this debate,” Allegranzi wrote in an email. But in weekly teleconferences, a large majority of a group of more than 30 international experts advising the WHO “have not considered the existing evidence sufficiently convincing to consider airborne transmissions as an important role in covid-19 proliferation.”
She added such a transfer “would have resulted in many more cases and even faster spread of the virus.”
Since the corona virus was first discovered in China in December, the understanding of how it spreads has evolved, resulting in the shift of guidelines for the use of masks.
First, WHO and the CDC said that masks were redundant for ordinary people and should be preserved for health workers. Later, CDC masking was recommended only for people with covid-19 symptoms.
Then in April, after it became clear that people without symptoms could spread the virus, the CDC suggested masks for everyone when physical distancing was difficult, a position that the WHO finally adopted.
Now that the outbreaks are spreading and the governors are ordering a new round of closures, almost all US states have made or recommended face coatings, mainly to prevent the carrier from spreading the disease.
Proponents of aerosol transfer said that properly worn masks would help prevent exhalation of exhaled aerosols and inhalation of the microscopic particles. But they said the spread could also be reduced by improving ventilation and dropping indoor air with ultraviolet light in roofing units.
Jose Jimenez, a University of Colorado chemist who signed the letter, said the idea of aerosol transmission should not scare people. “It’s not like the virus has changed,” he said. “We believe the virus has been transmitted in this way all the time, and knowing if it will help protect us.”
He and other researchers cited studies that support the idea of aerosol transfer is a serious threat.
As early as mid-March, a New England Journal of Medicine study found when the virus was interrupted in fog under laboratory conditions, it remained “viable and contagious” for three hours, which researchers said corresponded to as much as half an hour under real conditions.
It had already been established that some people, known as “super-distributors”, happen to be particularly good at exhaling fine material and producing 1,000 times more than others.
A new study found coronavirus RNA in the corridors near hospital rooms for covid-19 patients. Another issue was that aerosols loaded with the virus were discarded by floor cleaning equipment and by healthcare professionals who removed personal protective equipment.
Scientists in China found evidence of aerosols containing the coronavirus at two Wuhan hospitals.
It was the outburst among the choristers in Mount Vernon, Wash. – and a report on the Los Angeles Times incident – that first aroused interest in several aerosol advocates. Of 61 singers at a rehearsal on March 10, all but eight became ill, despite the members using hand cleansing and avoiding hugs or shaking hands. Two people though.
A team led by Shelly Miller, a University of Colorado professor of mechanical engineering, dug into the church gallery drawings, oven specifications, choir member locations and attendance hours. The researchers charted the movements of the singer, identified as the person who unknowingly brought the virus to practice.
Inhalation of aerosols “most likely to dominate infection change during this event,” the researchers wrote in a paper that underwent peer review, and concluded that the sick person, who had symptoms similar to a common cold, was unlikely to have spent time within 6 feet of many singers or having affected areas in common with them.
“We believe that shared air in the community hall, combined with high emissions of respiratory aerosol from singing, were important contributing factors,” the magazine said.
Eventually, researchers from a wide range of disciplines, including several who have studied the role of aerosols in the spread of influenza, SARS and other infectious diseases, joined forces to campaign for increased recognition of aerosol transmission.
They said that the corona virus is less contagious through the air than measles but that the risk of transmission goes up the longer the air stays stationary and the longer people continue to breathe.
In interviews, they said that WHO officials had unfairly set a higher bar to show aerosol spread than was required for the other two roads to be accepted. “For them, drops and touch are so obvious that they are proven, but airborne ones are so outlandish that a very high level of evidence is required,” Jimenez said.
Evidence would require a large number of healthy people to be exposed to aerosols emitted by covid-19 patients, says a researcher who would investigate it to be unethical.
Donald Milton, University of Maryland environmental health professor and an aerosol expert who wrote the letter together, said the average person breathes 10,000 gallons of air every day.
“You just need a contagious dose of 10,000 liters of coronavirus, and it can be very difficult to find it and prove it’s there, which is one of the problems we’ve had,” he said.
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