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July 10, 2020
Updated on July 11, 2020 at 17h34
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The COVID-19 transmissible by air ?
David Heymann
Infectious disease epidemiology, London School of Hygiene and Tropical Medicine
THE SCIENCE IN HIS WORDS / The last week, the world health Organization (WHO) has revised its position regarding the transmission of the COVID-19 by aerosol (droplets less than 5 microns in diameter that can stay a long time in the air). It is considered essentially impossible for Mr. and Mrs. All-the-World, but describes it now as a possibility in some circumstances. The british researcher David Heymann has had the following reaction to the result of this decision of the WHO.
“It is believed that the SARS-CoV2 [the virus that causes the COVID-19] is transmitted by droplets produced by coughing, sneezing or talking, yelling or singing. There are two types of transmission of SARS-CoV2 which are well understood : 1) the direct contamination when two faces touchewnt, or passes by a hand that will touch the face ; and 2) the transmission by droplets, either when a droplet containing the virus is projettée from one person to the other over a distance of approximately 1 meter, which is equivalent to the temporary suspension of the droplet in the air. In all cases, the virus is found in the droplet remain infectious as long as the droplet remains intact.
The aerosolization is a type of transmission by droplet that occurs to certain respiratory infections (such as measles) when droplets containing the virus are so small they can be carried by air currents over distances much larger than when the transmission is by droplet.
This could in theory happen with the SARS-CoV2 if the aerosols are driven by the fans or picked up by a system of recirculation of air such as an air conditioner, but this has not been well demonstrated. Research in order to have the heart net are underway.
There was some evidence in the laboratory demonstrating that the aerosol containing SARS-CoV2 can travel over 1 meter. These proofs are now important for the hypothesis that the aerosolization is possible, and if it is, then we would have to prove that this is indeed in practice.
But there are also evidence showing that outbreaks of SARS-CoV2 may be contained in tracing the sick and their contacts, and insulation. This suggests that even if the aerosol transmission occurs, it is not a mode of transmission major.
Experiments on animals may be useful to better understand all of this, and the hamster is a species that can be infected by the SARS-CoV2. Place hamsters in situations where only the aerosol transmission is possible may help. But in the end, it is really to the question of whether this happens really between human beings that need to be answered.”
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This text first appeared on the website of the Science Media Centre, uk. Reproduced with permission.
“The science in her words” is a forum where scientists of all disciplines can take the floor, either in open letters, or excerpts from books.
