A Midwestern Doctor

Because these fibrous clots are so unusual they have understandably provoked a great deal of confusion and uncertainty which has led many to grasp for rather unusual explanations over what is occurring. In situations like these, I believe that if a simple and comprehensive explanation can be identified, that represents the best approach for addressing this dilemma. Fortunately, one has been.

… In the study, a blood clotting simulation outside the body was created. Normal blood, blood from COVID-19 patients on the first day of symptoms before any treatment, and normal blood exposed to a low concentration of COVID-19 spike proteins were then exposed to a key clotting factor, thrombin. 

… In short, the authors found that when spike protein was added to blood samples, it caused irregular (misfolded) fibrous clots to form that were resistant to the enzymes researchers and the body (e.g. the digestive system) uses to break down protein structures. This most likely means the enzyme the body typically uses to break down fibrin clots cannot do so for these misfolded fibrous clots.