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Scientific evidence on the aerial transmission of the SARS-CoV-2 virus from different researchers all points in the same direction – that infectious aerosols are the main means of human-to-human transmission, according to experts.
Not that it’s without controversy.
The scientific transmission of aerosols “is clear, but not accepted in many circles,” said Trisha Greenhalgh, Ph.D. Medscape medical news.
“In particular, some of the evidence-based medicine movement and some infectious disease physicians are remarkably resistant to the evidence,” added Greenhalgh, a professor of primary care medical science at Oxford University, Oxford, UK.
“It’s very hard to see why, since all the evidence is accumulating,” Greenhalgh said.
“The scientific evidence for the spread of both near-field and far-field aerosols has been clear since the beginning of the pandemic, but there has been resistance to recognizing this in some circles, including medical journals,” Joseph G. Allen , DSc MPH, he said Medscape medical news when asked to comment.
“This is the week the dam broke. Three new comments have appeared … in top medical journals – BMJ, Lancet, JAMA – all making the same point that aerosols are the dominant mode of transmission, “added Allen, an associate professor of exposure assessment science at Harvard TH Chan School of Public Health in Boston, Massachusetts.
Greenhalgh and colleagues point to an increase in COVID-19 cases as a result of so-called “super-spreading” events, the spread of SARS-CoV-2 to people in various hotel rooms and the relatively lower transmission detected after outdoor events.
Top 10 reasons
They presented 10 scientific reasons that support air transmission in a comment published online on April 15 in Lancet:
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The dominance of airborne transmission is supported by long-distance transmission, observed at super-widespread events.
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Long-distance transmission was reported among COVID-19 quarantine hotel rooms, settings in which infected people never spent time in the same room.
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Asymptomatic people account for about 33% to 59% of SARS-CoV-2 transmission and could spread the virus through speech, producing thousands of aerosol particles and a few large drops.
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Transmission outdoors and in well-ventilated indoor spaces is lower than indoors.
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Nosocomial infections are reported in health care providers, where protective measures are addressed to large drops, but not to aerosols.
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Viable SARS-CoV-2 was detected in the air of the hospital rooms and in the car of an infected person.
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Investigators found SARS-CoV-2 in hospital air filters and construction pipelines.
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It’s not just about humans – infected animals can infect animals from other cages connected only by an air duct.
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No strong evidence rejects air transmission, and contact tracking supports secondary transmission in crowded, poorly ventilated interior spaces.
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Only limited evidence supports other means of transmitting SARS-CoV-2, including through fomites or large droplets.
“It simply came to our notice then [the evidence] to clarify the pros and cons. I was looking hard for evidence, but I couldn’t find any, “Greenhalgh said.
“Although other routes may contribute, we believe that the air route is likely to be dominant,” the authors note.
Evidence of airborne transmission was there very early, but the Centers for Disease Control and Prevention, the World Health Organization (WHO) and others reiterated the message that the main concern was drops and fomites.
Response to a review
The top 10 list is also a rejection of a systematic review funded by the WHO and published last month, which indicates inconclusive evidence for air transmission. The researchers involved in this review state that “the lack of recoverable viral culture evidence of SARS-CoV-2 prevents firm conclusions from being drawn about airborne transmission.”
However, Greenhalgh and colleagues note that “this conclusion and the wide circulation of the results of the analysis is worrying due to the public health implications”.
The current authors also claim that there is sufficient evidence of air transmission. “Policy should change. We don’t need more research on this issue; we need different policies,” Greenhalgh said. “We need front and center ventilation, air filtration when needed and more suitable masks worn whenever inside.”
Allen agreed that guidance did not always keep pace with science. “With all the new evidence gathered on air transmission last winter, there is still widespread public confusion about the modes of transmission,” he said. Allen is also commissioner of Lancet COVID-19 Commission and is the chair of the working group of the Committee on Safe Work, Safe Schools and Safe Travel.
“It wasn’t until last week that the CDC withdrew the ‘deep cleaning’ guide and rightly said the risk of touching surfaces is low,” he added. “Science has been clear in this regard for over a year, but official guidelines have recently been updated.”
As a result, many companies and organizations have continued to focus on “hygiene theater,” Allen said, “wasting resources on cleaning surfaces. Incredibly, many schools close for another full day each week for deep cleaning and some books are still in quarantine. the message that shared air is the problem, not shared surfaces, is a message that still needs to be strengthened. “
The National Institute for Health Research, the Council for Economic and Social Research and Wellcome support Greenhalgh research. Greenhalgh and Allen had no relevant financial relationships to disclose.
Damian McNamara it’s a staff Miami-based journalist. It covers a wide range of medical specialties, including infectious diseases, gastroenterology and critical care. Follow Damian on Twitter: @MedReporter.
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