@ Nadavegan: I don't know about covid, but I do not believe repeat infection has been demonstrated (not for lack of trying).

This is hypothesized to be a potential problem with some infections. Resolution without treatment confers (possibly transient) immunity in a way that resolution with treatment does not.

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Our God, will you not judge them? For we have no power to face this great multitude that is attacking us. We do not know what to do, but our eyes are on you. --2 Chron. 20:12