As we learn more about COVID-19 infection, venous blood clotting (venous thromboembolism) is a serious risk, particularly for those patients with severe disease and end up in the hospital. Dangerous clotting of arteries has been also seen in the severely ill. It has already been established for a long time that hospitalized patients are prone to deep venous thrombosis (DVT) and progress has been made in prevention with anticoagulation and pneumatic compression sleeves on the legs. Multiple clinical studies have demonstrated increased rates of DVT in COVID-19 patients. A paper that looked at existing studies identified that patients with COVID-19 have about a 20% for DVT and 19% for pulmonary embolism (a clot that travels to the lung which can be fatal).
The symptoms that patients need to look for is painful swelling of a limb, sudden shortness of breath or sudden pain and coldness of the hands or feet. Untreated DVT can lead to a pulmonary embolism. Arterial clotting can lead to loss of a limb.
Fortunately, vaccination can very significantly reduce the risk of severe disease and death due to Covid. Vaccination can also reduce the risks of blood clots. Although vaccination is a very rare cause of blood clotting, more clots are prevented by the reduced risk of severe Covid than are caused by vaccination.