[dTal]

Well, again, it's just unreasonable to expect masks - alone - to completely eliminate community spread. You've got to think in terms of the reproduction rate R. If it's above 1 you're losing, if it's below 1 you're winning. Each measure, like mask wearing, knocks a little fraction off R. The goal is to knock as many little fractions off as possible. It's totally possible for masks to "work" in the sense of knocking a worthwhile chunk off R, and yet have the public health strategy as a whole fail to bring it below 1.

The trouble is, managing R is an ongoing challenge. If you manage to get it below 1 and the rate of new infections decays to nearly nothing, great! But unless you completely shut the borders to prevent new seed infections, you have to keep doing whatever you were doing. If you relax, then R goes above 1, and exponential growth does its thing again and you're back where you started. There's a natural ceiling to the exponential growth - nobody quite knows why, though it's presumably something to do with acquired immunity - but it's a grim place to be.

I wouldn't look to the UK as an example of how to manage a pandemic. It has been bouncing along its infection ceiling ever since all measures were relaxed in July. I predict that the new mask mandates will have no detectable effect on infection rates; their modest effect on R will fail to bring it below 1, and rates will continue to "bounce along the top".