One of the enduring mysteries of COVID-19 is why it makes some people deathly sick but gives others only mild symptoms or none at all. We know that age matters, as do race; gender; and pre-existing medical conditions like high blood pressure, heart problems, and obesity. We also know that most people who succumb to the disease die because they develop severe pneumonia, also known as acute respiratory distress syndrome, or ARDS.
What we still don’t know, however, is what tips one COVID-19 victim toward ARDS but not another. Early in the pandemic, doctors noticed that, compared to forms of ARDS caused by other respiratory infections like flu, some features of COVID ARDS were peculiar. Patients were not only slower to develop the syndrome but also slower to recover, in some cases spending weeks on a ventilator. Often, their immune systems continued a ruinous battle against their own bodies – ravaging their lungs and choking them of oxygen – even after SARS-CoV-2, the virus that causes COVID-19, had been cleared from their systems.