Microscopic images of human stem cell–derived airway tissue models with cell nuclei (blue) and SARS-CoV-2–infected cells (green); tissue exposed to cigarette smoke (right) had 2 to 3 times more infected cells than non-exposed tissue (left). Credit: UCLA Broad Stem Cell Research Center/Cell Stem Cell
https://newsroom.ucla.edu/releases/how-smoking-worsens-covid-infection