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.
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
Key paragraph: Between Nov. 16 and Dec. 11, researchers found that infection rates were 37% lower in schools where teachers and staff members were required to wear masks. The difference between schools that did and did not require students to wear masks was not statistically significant.
A good recent article in NY Mag also discussing this issue, including the fact that the World Health Organization recommends against masking kids under six: https://nymag.com/intelligencer/2021/08/the-science-of-maski...
Many countries in Europe have decided against masking for any students in K-12 schools because it is unclear that the harms outweigh the benefits. The idea there is some "simple" scientific & research consensus on this is wrong.
Is it worth the cost? That’s a different question.
I’m not really opposed to masks in a classroom as a mitigation method, but if people believe it will significantly alter the trajectory of the infections I have a bridge to sell them.
Edit: Allow me to clarify - the research everyone is citing that says masking is effective in teachers and ineffective in students (the 37% number) predates both the delta variant and widespread infection in Southern states. Further, masking is understood etiologically as a prevention method and has been used successfully in other outbreaks and in other countries. Clinicians and policy makers as a rule work with incomplete data in an emerging situation, so unequivocally stating that masking kids in schools doesn't help is a very bad misrepresentation of both the data/research and the implications to policy.