Yep, it’s nothing more than a geometry problem. The holes in commonly-worn masks, including surgical masks, range from about 1,000 to 5,000 times larger than the Wuhan coronavirus. As you say, using a mask to prevent COVID is as absurd as trying to keep mosquitos out of your yard with a chain link fence. Even the vaunted N95 mask has been proven to have no effect on preventing transmission. Yet there are still many, even a few on here, who cling to a superstitious faith in masks. Keeping a rabbit’s foot with them would be just as effective.