The predisposition of smokers to COVID-19 infection: A mini-review of global perspectives

Both SARS-CoV-2 and smoking tobacco adversely impact the respiratory system, damaging the airways and impairing lung function. While some studies have identified a positive association between smoking and increased susceptibility to COVID-19 infections, a few papers have concluded that smokers may be protected against such infections. Given these contradictory findings, there is an ongoing debate in the scientific community about whether or not smokers have a stronger predisposition towards COVID-19 infections. Through this mini-review, we aimed to study the relationship between tobacco smoking and COVID-19 infections by conducting a comprehensive literature search of peer reviewed articles that reported on the effects of smoking on COVID-19 susceptibility and were published globally over the past two years (January 2020-April 2022). Our search identified 31 articles that demonstrated a positive or strong relationship between smoking and COVID-19, while 13 articles had contrasting results. Additionally, we evaluated mechanistic studies suggesting that, among smokers, angiotensin-converting enzyme-2 genes are upregulated, facilitating easier binding of SARS-CoV-2, thereby increasing the risk of COVID-19 infection. In conclusion, the majority of studies in this area to date provide evidence of a strong relationship between smoking and COVID-19 infection; however, the strength of this association may vary across the smoking behaviors of differing populations. Future work could involve a meta-analysis of studies focusing on susceptibility to COVID-19 infection for different types of tobacco product smokers, which would result in a more comprehensive understanding of the predisposition of smokers towards COVID-19 infections.