'Could it not be that smokers have developed an immune system to this virus? 'Some evidence suggests that gene expression and subsequent receptor levels are elevated in the airway and oral [cells] of current smokers​, thus putting smokers at higher risk of contracting SARS-CoV-2. 'This could, at least partly, explain the association between smoking and COVID-19 severity among hospitalized patients. One doctor replied that their smoking frequency was so low because some patients were literally too sick to answer the question.'So... 'I don't think that there's any convincing evidence that smoking protects against coronavirus.