https://www.scientificamerican.com/article/blood-clots-are-mysteriously-tied-to-many-coronavirus-problems/

Purple rashes, swollen legs, clogged catheters and sudden death—blood clots, large and small, are a frequent complication of COVID-19, and researchers are just beginning to untangle why. For weeks, reports have poured in of the disease’s effects throughout the body, many of which are caused by clots. “This is like a storm of blood clots,” says Behnood Bikdeli, a fourth-year cardiology fellow at Columbia University in New York City. Anyone with a severe illness is at risk of developing clots, but hospitalized patients with COVID-19 appear to be more susceptible.

Studies from the Netherlands and France suggest that clots appear in 20% to 30% of critically ill COVID-19 patients. Scientists have a few plausible hypotheses to explain the phenomenon, and they are just beginning to launch studies aimed at gaining mechanistic insights. But with the death toll rising, they are also scrambling to test clot-curbing medications.