I do insist. You're making the claim that WHO / CDC knew that masks work. So, let's see the evidence that you think they had.
> If they didn't believe that masks worked, why would they do that?
Because a healthcare professional stuck in a room with symptomatic people is a different situation to a member of the public walking around.
Especially because HCPs are trained to use masks, they use them in combination with other PPE and routine handwashing; their PPE is made to standards and tested to make sure it complies with those standards; HCPs are audited on their use of handwashing and PPE.
> If they didn't believe that masks worked, why would they do that?
Because a healthcare professional stuck in a room with symptomatic people is a different situation to a member of the public walking around.
Especially because HCPs are trained to use masks, they use them in combination with other PPE and routine handwashing; their PPE is made to standards and tested to make sure it complies with those standards; HCPs are audited on their use of handwashing and PPE.