The World Health Organisation on Thursday released new guidelines on the transmission of the novel coronavirus that acknowledge some reports of airborne transmission of the virus that causes Covid-19, but stopped short of confirming that the virus spreads through the air.
In its latest transmission guidance, the WHO acknowledged that some outbreak reports related to indoor crowded spaces have suggested the possibility of aerosol transmission, such as during choir practice, in restaurants or in fitness classes.
But the WHO said more research is “urgently needed to investigate such instances and assess their significance for transmission of Covid-19”.
Based on its review of the current evidence, the WHO said the novel coronavirus that causes Covid-19 spreads between people through direct or indirect contact with contaminated surfaces or close contact with infected people who spread the virus through saliva, respiratory secretions or droplets released when an infected person coughs, sneezes, speaks or sings.
The report follows an open letter from scientists who specialise in the spread of disease in the air – so-called aerobiologists – that urged the global body to update its guidance on how the respiratory disease spreads to include aerosol transmission.
“This is a move in the right direction, albeit a small one. It is becoming clear that the pandemic is driven by super-spreading events, and that the best explanation for many of those events is aerosol transmission,” said Jose Jimenez, a chemist at the University of Colorado who signed the letter, which was published on Monday in the journal Clinical Infectious Diseases.
How frequently the coronavirus spreads by the airborne or aerosol route – as opposed to by larger droplets in coughs and sneezes – is not clear.
In a press briefing on Thursday, Dr Anthony Fauci, director of the US National Institute of Allergy and Infectious Diseases, said there is not a lot of solid evidence yet on airborne transmission of Sars-CoV-2, but said: “I think it’s a reasonable assumption that it does occur.”
Although incomplete, Fauci said the evidence so far is “the fundamental basis for why we are now so intent on getting people – particularly people without symptoms – to wear masks. To be able to see if we can mitigate against that”, he said.
Only a very small number of diseases are believed to be spread via aerosols, or tiny floating particles. These include measles and tuberculosis – two highly contagious diseases that require extreme precautions to prevent exposure.
WHO guidance acknowledges that airborne transmission of the novel coronavirus can occur during specific medical procedures that generate aerosols, such as when performing intubation.
In these circumstances, they advise medical workers performing such procedures to wear heavy-duty N95 respiratory masks and other protective equipment in an adequately ventilated room.
Any change in the WHO’s assessment of risk of transmission could affect its current advice on keeping one-metre (3.3-foot) physical distancing.
Governments, which also rely on the agency for guidance, may also have to adjust public health measures aimed at curbing the spread of the virus.
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