PF4 and COVID-19: Through the vaccine adenoviral non-replicating vectors (AVV), the COVID-19 vaccines may (i) spread rapidly into the blood stream, (ii) promote the early production of high levels of IL-6, (iii) interact with erythrocytes, platelets, mast cells, and endothelia, (iv) favour the presence of extracellular DNA at the site of injection, and (v) activate platelets and mast cells to release PF4 and heparin [36].