[HPsquared]

I wonder how much of the improvement was due to reversion to the mean. When bringing everyone back, you would expect a sharp peak of infections which would decay to normal levels after a while - filters or not. I'm sure they do still have some positive effect though.

[Balgair]

Anecdotally: it was a big effect.

Rigorously: no way to tell now, the time has passed.

Likely: you're right. But what little staff is there from pre-covid says that they have helped a lot too.

Reality: here's $500/wk and my kid, in return I get really sick for a year no matter what.