Maybe the smoke coats the lungs inner walls making it where the viral particles are less likely to penetrate.
It appears as those nicotine hinders the virus ability to penetrate cell well and move through body, secondly the nicotine appears to act as an immune system suppressant and keeps the bad immune reactions down.
If so that it aint getting me-—I use a can a day of some of the strongest swedish snus available (imported) and get the equivalent nicotine of 8-10 packs of smokes a day.