The additives in cigarettes have been shown to dilate lung airways, suppress coughing, and disguise symptoms of illness:

https://www.verywellmind.com/cigarette-additives-2824737

Perhaps the additives are keeping COVID-19 patients alive by supporting breathing in difficult circumstances? There are hundreds of additives so figuring out if any of them help would be difficult:

https://ec.europa.eu/health/scientific_committees/emerging/d...