Smoking Association with Transmission and Mortality of COVID-19

Abstract

Introduction: Given the unclear evidence about smoking in COVID-19-infected patients, we conducted a comprehensive review to determine the association between smoking and disease severity in COVID-19-infected patients by including all eligible studies. Systematic searching of databases for available evidence and careful definition of disease severity was performed for a rigorous summary of the conclusions.
Methods: To find relevant studies, scientific databases including Embase, PubMed, Science Direct, Google Scholar, and Cochrane Library databases were systematically searched. All relevant articles that reported clinical characteristics and epidemiological information on smoking among COVID-19-infected patients were included in the analysis. All articles with any design (randomized controlled trials and observational studies) were included. The primary outcome was disease severity among COVID-19 patients with a history of smoking. The secondary outcome was death among COVID-19 patients with a history of smoking.
Results: Studies reporting a low rate of smoking have been criticized for the poor quality and retrospective collection of smoking status data, the comparison of smoking of subjects covid-19 to the smoking of the general population sometimes without taking into account sex and age, and for having included only symptomatic or in-hospital subjects, creating possible selection bias. In this context, it is important to further explore the relationships between smoking and covid-19 and to determine whether these relationships could reflect an effect of nicotine or smoke itself. Among 8910 patients hospitalized for covid-19 (low smoking rate, 6% smokers) researchers observed a greater risk of death for current smokers than non-smokers or former smokers.

Conclusions: Smoking is confirmed to be a risk factor for the negative progression of COVID-19, particularly in disease severity and death. Both current and former smokers have higher odds of disease severity than never-smokers. Given the well-established harm associated with tobacco use, smoking cessation is recommended for all smokers and the avoidance of second-hand smoke by non-smokers.