Ironically, WHO and CDC have done bad messaging on both sides of this. I get slammed every time I bring this up now, because the issue is politicized and, let's be honest, pretty traumatic as well. But I think it's important so I'll keep trying.
Everyone should have been masking up as soon as possible in the pandemic. Case counts were low, we didn't know much about the route of transmission, and we also thought it was even more dangerous than it turned out to be. Precautions were indicated, but health authorities were decrying mask use as late as the end of March.
But it turns out that the primary vector is aerosols, not droplets or fomites. Any mask will mitigate droplet contamination, and the resulting fomites: this is why influenza has practically disappeared, masking is very effective against influenza, where those are the primary vector.
But no mask will do much to filter aerosols on exhalation. That's simply not how they work, positive pressure puts most of the gasses out through the sides of the mask. Even a P100 filter with cartridges won't do it, that's why they have a vent, otherwise the face seal would be broken every time one exhales. To be generous, I'll say that a cloth mask catches 30% of aerosols. It doesn't, but say it does: that's not nearly good enough. Which case counts after universal masking mandates illustrate quite clearly: they rise, and fall, and the masks don't have anything to do with it.
A good mask will filter some aerosols when inhaling: but a cloth mask won't. So once aerosols were identified as the culprit, WHO and CDC should have emphasized air filtration, which is quite effective, limiting the number of people indoors on the basis of how many air exchanges a HEPA or ULPA filter was capable of doing. Messaging should have emphasized that cloth and surgical masks are completely useless, and that at-risk people should stay home, and if they can't, should get a proper mask (KN94, (K)N95, P100) and learn how to use it. COVID doesn't survive on surfaces very long, so reuse is more-or-less ok, and there were plenty of proper masks by June, which is when these facts were available. If WHO and CDC had listened to them.
I vape, so I can illustrate this to myself quite easily: I can hit the vape through a cloth mask, but not a KN94. And with any mask, I can take a hit, put it on, and exhale a visible cloud of, yep, aerosols, around the side of the mask.
I still wear a KN94 indoors, it's the best I can do. But I'm walking around in indoor spaces with no HEPA filters, surrounded by people who are unprotected, just wearing a talisman. This was preventable.