My thoughts on WHO's updates:
who.int/publications-d… is an improvement
who.int/news-room/q-a-… is still in denial. See thread below /1
who.int/publications-d… is an improvement
who.int/news-room/q-a-… is still in denial. See thread below /1
WHO's updated scientific brief on transmission of COVID-19 is a step in the right direction because they now acknowledge that airborne transmission may be occurring outside of specialized medical procedures, although they remain fixated on medical procedures as... /1
the main source of aerosols when we know they are generated by normal respiratory activities such as breathing, talking, singing, laughing, etc. /2
They encourage the use of face coverings when physical distancing is not possible, but I would like to see WHO make a stronger recommendation for use of face coverings at all times indoors, except in one's own residence or when in a room by oneself /3
because there is increasing evidence that face coverings are very effective at slowing transmission, and they are a relatively inexpensive intervention. /4
I am disappointed to see that WHO is still relying on an outdated definition of droplets and aerosols, separated at a cutoff of 5 microns. A 5-micron droplet can remain floating in the air for half an hour. /5
It would be better to distinguish transmission routes on the basis of how the person is exposed. Droplets land on the body, while aerosols are inhaled into the respiratory system. /6
With this definition, a size cutoff of somewhere in the range of 50-100 microns is more appropriate. /7
Although WHO focuses on airborne transmission at long distances, I would like to emphasize that transmission by inhalation of aerosols is of greater concern at close contact and when people are in the same room. /8
At close contact, transmission by aerosols might be as important or more important than droplet spray transmission because an infected person's respiratory plume is most concentrated right in front of their face. /9
Additionally, in poorly ventilated rooms, respiratory aerosols can build up in the air and pose a risk to others in the same space. /10
