1/ We are focussed on ventilation quantity to reduce risk of COVID-19 and that is not all that matters.

2/ Ventilation pathway matters too. Does ventilation air get contaminated by another source before it gets to you?

3/ Ventilation velocity matters. Airflows can cause/enhance resuspension from surfaces.

4/ Ventilation influences humidity. One of my fears about next winter is that we are going to ventilate/heat more leading to more spread of droplets and increased susceptibility.

5/ Ventilation influences comfort. Occupants will defeat ventilation changes if it negatively influences their comfort.

6/ Ventilation brings in outdoor air contaminants. In some environments we are trading one harm for another.

7/ Practical advice: Ventilate well, but carefully. Go to Andy and Lisa's webinar tomorrow https://www.isiaq.org/docs/COVID-19_PersilyNg_May19.pdf

8/ I should have added 2 things. Ventilation cross contamination (exhaust air getting reentrained) and mixing causing increased indoor dispersion are other potential ventilation issues to consider.