Six months after a pandemic that killed more than half a million people, more than 200 scientists from around the world are challenging the official view of how the coronavirus spreads.
The World Health Organization and the US Centers for Disease Control and Prevention say you only need to worry about two types of transmission: inhalation of respiratory droplets of an infected person in your immediate vicinity or – less common – touching a contaminated surface and then your eyes, nose or mouth.
But other experts maintain that the guidance ignores mounting evidence that a third pathway also plays a significant role in contagion.
They say that several studies show that particles known as aerosols – microscopic versions standard respiratory droplets – can stay in the air for long periods and floats dozens of feet, making dangerous poorly ventilated environments, buses and other confined spaces, even when people are two meters apart.
“We are 100% sure of that,” he said Lidia Morawska, professor of atmospheric sciences and environmental engineering at Queensland University of Technology in Brisbane, Australia.
She argues in an open letter to WHO accusing the United Nations agency of not issuing appropriate warnings about the risk. 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 that aerosol transmission appears to be the only way to explain several “super propagation” events, including infection of snack bars in a restaurant in China who sat at separate tables and members of the Washington state choir who took precautions during a rehearsal.
WHO officials have recognized that the virus can be transmitted through aerosols, but claim that it occurs only during medical procedures as an intubation that can vomit large amounts of microscopic particles. CDC officials did not respond to several requests for comment.
Dr. Benedetta Allegranzi, one of WHO’s leading experts in infection prevention and control, said in response to questions from The Times that Morawska and his group presented theories based on laboratory experiments, rather than field evidence.
“We value and respect your opinions and contributions to this debate,” wrote Allegranzi in an email. But in weekly teleconferences, the vast majority of a group of more than 30 international experts who advise WHO have “did not find the existing evidence sufficiently convincing to consider overhead transmission as having an important role in the spread of COVID-19 “.
She added that this transmission “would have resulted in many more cases and an even faster spread of the virus”.
Since the coronavirus was first detected in China in December, the understanding of how it spreads has evolved considerably, resulting in change guidelines about wearing masks.
At first, WHO and the CDC said that masks were overkill for ordinary people and should be retained for healthcare professionals. Later, the CDC recommended masks only for people with symptoms of COVID-19.
Then, in April, after it became clear that people without symptoms could also spread the virus, the CDC suggested masks for everyone when physical distance was difficult, a position that WHO finally adopted.
Now, when outbreaks proliferate and governors order a new round of closings, almost every state in the U.S. has made mandatory or recommended facial coverage, primarily to prevent users from spreading the disease.
Proponents of aerosol transmission said masks used correctly would help prevent the escape of exhaled aerosols as well as inhaling the microscopic particles. But they said the expansion could also be reduced, improving ventilation and eliminating indoor air with ultraviolet light in ceiling units.
Jose Jimenez, a University of Colorado chemist who signed the letter, said the idea of transmitting aerosols should not scare people. “It’s not like the virus has changed,” he said. “We believe that the virus has been transmitted this way all the time, and knowing about it helps to protect us.”
He and other scientists cited several studies supporting the idea that aerosol transmission is a serious threat.
In mid-March, a study in the New England Journal of Medicine found that when the virus was suspended in the fog under laboratory conditions, it remained “viable and infectious” for three hours, which the researchers said was equivalent to half an hour in normal conditions. the real world.
It has already been established that some people, known as “super spreaders”, are especially good at exhaling fine materials, producing 1,000 times more than others.
A recent study found coronavirus RNA in corridors near the hospital rooms of patients with COVID-19. Another raised concerns that aerosols loaded with the virus would be launched by floor cleaning equipment and health professionals removing personal protective equipment.
Researchers in China found evidence of aerosols containing the coronavirus in two hospitals in Wuhan.
It was the outbreak among choir members in Mount Vernon, Washington – and a report on the incident in The Times – that sparked the interest of several of the aerosol proponents. Of the 61 singers in a March 10 rehearsal, all but eight were sick, although members used hand sanitizer and avoided hugging or shaking hands. Two people died.
The researchers looked at ventilation in this church hall, where members of Skagit Valley Chorale gathered for a trial that led to a fatal outbreak of COVID-19.
(Karen Ducey / For the Times)
A team led by Shelly Miller, professor of mechanical engineering at the University of Colorado, researched the plans of the church hall, the furnace specifications, the location of the choir members and the opening hours. The researchers diagrammed the movements of the singer who was identified as the person who unwittingly took the virus to practice.
Aerosol inhalation “probably dominated the transmission of infection during this event”, the researchers wrote in an article undergoing a peer review, concluding that the sick person, who had symptoms similar to a common cold, would hardly spend time at six feet from many singers or would touch surfaces in common with them.
“We believe that air sharing in the fellowship hall, combined with high respiratory aerosol emissions from the corner, were important contributing factors,” said the newspaper.
Eventually, researchers from a wide spectrum of disciplines, including several who studied the role of aerosols in the spread of flu, SARS and other infectious diseases, have joined forces to campaign for greater recognition of aerosol transmission.
They said that coronavirus is less contagious by air than measles, but that the risk of transmission increases, the longer the air remains stagnant and more people continue to breathe.
In interviews, they said that WHO officials unfairly set a higher level for showing the spread of aerosol than is necessary for acceptance of the other two routes. “For them, the droplets and touch are so obvious that they are proven, but the air is so strange that it needs a very high level of evidence,” said Jimenez.
The test would require exposing a large number of healthy people to aerosols emitted by patients with COVID-19, a study that scientists said would be unethical.
“You just need an infectious dose of coronavirus in 10,000 liters, and it can be very difficult to find it and prove it is there, which is one of the problems we have had,” he said.