There have been indications that smokers and people in India and possibly (?) China are less likely to suffer serious syptoms from corona virus.
Although several explanations are possible, and the statistics may well be faulty either by accident or design, taking these facts at face value one thing common to both is elevated CO levels, from the tobacco smoke and from traffic and wood fire pollution.
It isn't commonly known, but the body uses CO for various purposes such as part of its nerve signalling mechanism. See https://en.wikipedia.org/wiki/Carbon_monoxide :
Carbon monoxide is produced naturally by the human body as a signaling molecule. Thus, carbon monoxide may have a physiological role in the body, such as a neurotransmitter or a blood vessel relaxant. Because of carbon monoxide's role in the body, abnormalities in its metabolism have been linked to a variety of diseases, including neurodegenerations, hypertension, heart failure, ..
The natural role of CO in the body (aside from its toxic effects) was discovered only in 1993, and is still an active area of research with many unknowns.
Now some Covid symptoms, such as loss of taste and smell (as seen to some extent in smokers), and often a general feeling of muddle headedness for some time during recovery are similar to symptoms and chronic after effects of CO poisoning, e.g. https://www.st-va.ncbi.nlm.nih.gov/pmc/articles/PMC3850907/
A possible implication of this is that the CV virus somehow prompts the body to produce excess CO, to a toxic extent. So my question as in the title is whether (1) This is a likely explanation and (2) If so, could its effects be ameliorated in advance by building up a small degree of CO tolerance under controlled conditions?