An open letter from 239 scientists in 32 countries has accused the World Health organisation of underestimating the possibility of airborne coronavirus transmission.
The current scientific position is that coronavirus is mainly transmitted in liquid droplets produced when someone coughs, sneezes or even breathes heavily. These droplets fall to surfaces, hence the emphasis on the importance of hand-washing to prevent transmission.
But the WHO has now admitted that there is growing evidence that the virus can be transmitted in smaller particles which become airborne.
The danger of airborne coronavirus is thought to be particularly high in enclosed spaces with poor ventilation.
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The open letter begins: “We appeal to the medical community and to the relevant national and international bodies to recognize the potential for airborne spread of COVID-19. There is significant potential for inhalation exposure to viruses in microscopic respiratory droplets (microdroplets) at short to medium distances (up to several meters, or room scale), and we are advocating for the use of preventive measures to mitigate this route of airborne transmission.
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Risk of exposure
“Studies by the signatories and other scientists have demonstrated beyond any reasonable doubt that viruses are released during exhalation, talking, and coughing in microdroplets small enough to remain aloft in air and pose a risk of exposure at distances beyond 1 to 2 m from an infected individual.
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“For example, at typical indoor air velocities, a 5μm droplet will travel
tens of meters, much greater than the scale of a typical room, while settling from a height of 1.5 m to the floor.
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“Several retrospective studies conducted after the SARS-CoV-1 epidemic demonstrated that airborne transmission was the most likely mechanism explaining the spatial pattern of infections.”
“We wanted them to acknowledge the evidence,” said Jose Jimenez, a chemist at the University of Colorado who signed the paper, talking to the Reuters news agency.
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“This is definitely not an attack on the WHO. It’s a scientific debate, but we felt we needed to go public because they were refusing to hear the evidence after many conversations with them,” he said.
Important implications
Another signatory, Professor Benjamin Cowling of Hong Kong University, told the BBC that the findings about airborne coronavirus had “important implications”, and may affect guidelines for indoor spaces.
“In healthcare settings, if aerosol transmission poses a risk then we understand healthcare workers should really be wearing the best possible preventive equipment… and actually the World Health Organization said that one of the reasons they were not keen to talk about aerosol transmission of Covid-19 is because there’s not a sufficient number of these kind of specialised masks for many parts of the world,” he said.
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“And in the community, if we’re thinking about aerosol transmission being a particular risk, then we need to think about how to prevent larger super spreading events, larger outbreaks, and those occur in indoor environments with poor ventilation, with crowding and with prolonged close contact.”
Dr Benedetta Allegranzi, Technical Lead of the WHO’s Infection Prevention and Control Hub and Task Force, said of the possibility of airborne coronavirus transmission: “There is emerging evidence in this field and we have to be open to its implications regarding the modes of transmission and the precautions that need to be taken.”
Aerosol transmission
Dr Marian Van Kerkhove, Technical Lead COVID-19 on the WHO Health Emergencies programme, added: “Many of the signatories are engineers, which adds to growing knowledge of the importance of ventilation…we have been talking about aerosol transmission as well as other forms of transmission…we have engaged with a large number of groups to try to consolidate the growing knowledge around transmission.”
Dr Anthony Fauci, director of the US National Institute of Allergy and Infectious Diseases, said that while there had been studies of aerosolised transmission of viruses including SARS, there was not “a lot of definitive evidence” that coronavirus can be transmitted through airborne spread. While he believed it was not a major factor, he also warned that it should not be ruled out.
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Dr Fauci described surroundings such as indoor bars as “the perfect setup for the spread of infection”, and emphasised the importance of health fundamentals such as masking, distancing and washing hands. He advocated the closure of bars, describing it as “a giant step in interfering with the spread of infection in your community.”
Coronavirus transmission
The evidence or airborne coronavirus presented by the scientists in the letter, published by Oxford University Press on behalf of the Infectious Disease Society of America, will now have to be evaluated. What is perhaps most significant is that it suggests that the 2m separation rule applied in the UK, or 1m rule applied elsewhere in the world, might be entirely inadequate to protect against airborne coronavirus transmission in enclosed spaces.
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You can read here the open letter from 239 scientists in 32 countries accusing the World Health Organisation of underestimating the possibility of coronavirus being transmitted through the air.
