a review on suggested mechanisms in thrombocytopenia and thrombosis following chadox1 ncov-19 vaccination

Background: chadox1 ncov-19 vaccine is a viral vector-based vaccine with desirableprotection (about 70.4%, two weeks after the second dose). few reports were releasedon thrombocytopenia associated with thrombotic events shortly after the chadox1ncov-19 vaccination. however, the exact pathophysiologic mechanism of this vaccineinducedthrombotic complication has not yet been elucidated. vaccine-induced thromboticthrombocytopenia syndrome (vitts) is associated with detecting anti-platelet factor 4(pf4) antibodies that are not yet linked to previous exposure to heparin.materials and methods: in the current review, based on relevantly reported cases,possible mechanisms are suggested on the relationship between the anti-platelet factor 4(anti-pf4) antibody assays, previous exposure to heparin, and the involved mechanisms ofpost-vaccination thrombocytopenia and thrombotic events, which might help the expertsfor selecting the appropriate therapeutic measures.results: possibly involved mechanisms in vitts after chadox1 ncov-19 vaccinationinclude binding of anti-pf4 antibodies to heparin/pf4 complex or receptor-binding domain(rbd) protein-pf4 complex. another mechanism could be the binding of anti-rbdantibodies to the rbd protein-pf4 complex. finally, anti-rbd or anti-pf4 antibodies maybind to the heparin-rbd protein-pf4 complex. the binding of either of the mentionedantibodies to these complexes via the fc/angiotensin-converting enzyme 2 receptors cancause activation/removal of platelets leading to thrombocytopenia and thrombosis.conclusion: the suggested mechanisms in this article provide a relationship betweenthe results of anti-pf4 antibody assays, previous exposure to heparin, and the involvedmechanisms of post-vaccination thrombocytopenia and thrombotic events, which mighthelp the experts in selecting the therapeutic measures.