By Michael Le Page
Aurelien Meunier/Getty Images
Over 200 scientists have called for the world to take more precautions against the airborne transmission of the coronavirus. While the virus is known to spread through the air via large droplets produced when people cough or sneeze, they say it can also be spread by smaller droplets known as aerosols that can linger in the air. Preventing this means ventilating buildings and avoiding overcrowding.
“Hand-washing and social distancing are appropriate, but, in our view, insufficient to provide protection from virus-carrying respiratory microdroplets released into the air by infected people,” states a letter written by Lidia Morawska at Queensland University of Technology in Australia. It has been signed by 239 researchers.
The letter also calls for international bodies such as the World Health Organization (WHO) to acknowledge the possibility of this type of airborne spread and suggests precautions against it.
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Morawska and others have made similar calls in recent months, but it is especially important to address the issue now that people in many countries are returning to workplaces, restaurants and pubs, says signatory Julian Tang at the University of Leicester in the UK. Improving ventilation will reduce the risk, he says. “You can’t rely on people wearing masks.”
The letter has been attacked by some researchers. “I don’t think the overall conclusions are correct,” says Paul Hunter at the University of East Anglia, UK. “They are potentially damaging.”
He says the letter could cause confusion among the public and that taking measures to prevent aerosol spread could give people a false sense of security, making them less likely to take other steps, such as washing their hands.
The WHO uses the term “airborne spread” only for transmission by droplets that are less than 5 micrometres in diameter. These can remain aloft for longer than the larger droplets produced by an infected person coughing or sneezing.
The WHO’s position is that there is only a risk of spread of the coronavirus via aerosols when medical procedures such as intubation produce them, but many researchers think it can also be spread by aerosols produced when people talk, laugh or sing.
However, few scientists think that coronavirus aerosols can infect anyone far from the source. “The letter is not arguing for long-range transmission,” says signatory Catherine Noakes at the University of Leeds, UK.
People are only likely to be infected this way if they are close enough to a person with the coronavirus for long enough to breathe in a large number of virus particles, she says. This is much more likely in poorly ventilated spaces where particles build up.
The main point of contention is what proportion of cases are caused by aerosol spread. “I think there probably is some airborne transmission,” says Hunter. “The issue is whether that is important enough to justify additional control measures.”
No one knows for sure because it is hard to tell how people get infected. It is usually assumed to be via touch or droplets rather than aerosols, says Morawska.
Tang says the WHO doesn’t want to acknowledge airborne transmission of this sort because preventing it involves more expensive and disruptive control measures – such as medical staff wearing N95 masks – that many countries would struggle to afford. However, the letter doesn’t call for any changes in hospital practices.
The WHO gave a standard response when asked for comment on the letter: “We are aware of the article and are reviewing its contents with our technical experts.”
Journal reference: Clinical Infectious Diseases, DOI: 10.1093/cid/ciaa939
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