Are you sure nicotine is the active ingredient here that's mitigating the COVID? It's certainly what smokers crave but the COVID virus could be affected by some other part of the smoke.
Sure? I am sure of very little. My priors (i.e. my physical model) favor the theory that nicotine prevents infection by blocking ACE2 receptors. I have no posterior inferences to confirm or refute the hypothesis.
Smokers crave something else than nicotine. It is just a convenient boogeyman. There are studies where tobacco addicts are given the choice between getting nicotine intravenously or smoking denicotinized cigarettes. An overwhelming majority prefers smoking denicotinized cigarettes.
