My conclusion is that the CDC has been deliberately lying to the public for reasons that seemed so morally right to them that they overrode the usual scientist's commitment to the truth. Clearly, masks were thought to be effective enough at protecting the wearer that they needed to be saved for the people who needed them most. So the general public was told that they were COMPLETELY INEFFECTIVE so they wouldn't hog them. But this resulted in a cascade of lies and half truths so confusing that I don't think anybody knows what's real now, least of all the health care workers that they were trying to protect. So now we have nurses running out to Home Depot and buying dust masks for use in COVID wards - surely that isn't going to work, is it? But it probably works better than homemade masks made out of t-shirts. Or maybe not. Who knows?