People who have COVID-19 have microvascular thrombosis in the lungs. Many of the ground-glass abnormalities witnessed on chest CT scans are actually pulmonary emboli, not pneumonia.
These people have transient ischemia of the small vasculature of the alveoli in their lungs. And then, they pump in concentrated oxygen, into tissues that have been ischemic for a while, and people get reperfusion injury. They get reperfusion injury very, very severely, because the virus accelerates lipid peroxidation by disabling people's antioxidant enzymatic pathways. Nrf2 down-regulation means no glutathione peroxidase and other, similar enzymes to prevent ROS buildup.