We may not have trials or studies (these things take time) to back a very certain and/or specific claim such as "do masks prevent the spread of Covid 19?" What we do have, is fundamental knowledge and common sense and so typically, in a clinical setting we ask these questions when any new situation arises (as it happens often in medicine):
- Does this reccomendation cause more harm than good?
- is there even a slight chance that this clinical decision would increase the percentage chance of survival?
- is it worth the inconvenience it could cause?
This is called Clinical Reasoning. Thinking critically and clinically is a core tenet of the field.
"Research shoes masks are still effective even when spending the whole day in the same room"
I'm not aware of any evidence that this is the case and I worry that people are putting too much stake in masks when really social distancing is much more effective than masks ever will be.
This is a common attribute of infections and is really more of a math issue than anything SARS-specific. The bigger the initial dose, the sooner it will get to the impact stage, and the less prepared your immune system will be at that time.
https://www.nature.com/articles/s41598-020-72798-7 It does note that non-medical (e.g. cloth) masks may be less effective, but whether those are used a lot seems to depend on environment (nobody seems to use them here). Edit: One more for cloth masks https://www.nature.com/articles/jes201642
My understanding was that masks were primarily effective at preventing high viral load droplets from spreading the virus during short interactions.
I don't have any source to prove that to be the case because data on the effectiveness of masks seems frustratingly sparse.