A June 2020 study reported that national smoking rates inversely correlated with COVID-19 mortality. In countries with hot weather, each percentage point increase in smoking rate was associated with a 0.147 per 100,000 population decrease in mortality
A systematic review and meta-analysis of 22 studies, however, found smoking modestly increased the risk of more severe symptoms among hospitalized COVID-19 patients, especially among younger nondiabetic patients
A September 2020 review found patients with a history of smoking (either current or former) had, on average, a 91% higher odds ratio of suffering more severe COVID-19 illness than patients who had never smoked
Teens and young adults who smoked conventional and/or e-cigarettes were 2.6 to nine times more likely to test positive for SARS-CoV-2. Those who vaped were also 5 times more likely to exhibit COVID-19-related symptoms and receive a COVID-19 diagnosis than nonusers
Recent research shows nicotine increases ACE2 expression in bronchial epithelial cells