Clinicians are reporting that some young patients are having strokes due to blood clots. Critical care doctors are beginning to give severe patients preventive anticoagulation therapy to prevent or help dissolve these clots. There are many articles on this but here is one:
Abnormal Clotting and COVID-19
Abnormal clotting, apparently resulting from endothelial damage, has been described in patients with severe COVID-19 disease, and Chinese clinicians recommend initiating prompt anticoagulation therapy in all severe COVID-19 patients.