If you insist I'm happy to go hunting for studies, but let's remember that the CDC from the start was advocating that people reserve masks for healthcare workers. If they didn't believe that masks worked, why would they do that?

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.