STAT3 and COVID-19: Patients may have markedly impaired oxygenation early in the course of the disease, which is said to be due to increased activity of the coagulation system; plasminogen activator inhibitor-1 expression is increased in older adults and in people with hypertension, obesity, and diabetes, which are risk factors for COVID-19; and in severe cases of COVID-19, STAT3 and plasminogen activator inhibitor-1 activation is escalated, leading to catastrophic consequences.