Rare and unusual adverse thrombotic events and thrombocytopenia may be associated with COVID-19 vaccines from AstraZeneca and Johnson & Johnson (J&J), so called vaccine-associated immune thrombotic thrombocytopenia (VITT). VITT resembles autoimmune heparin-induced thrombocytopenia, a well-known prothrombotic disorder caused by platelet-activating antibodies that recognize multimolecular complexes between cationic platelet factor 4 and anionic heparin or other triggers. Patients may develop severe headache, abdominal pain, leg pain, shortness of breath, petechiae, or new or easy bruising, etc. within three weeks after vaccination. As with heparin-induced thrombocytopenia, the administration of the anticoagulant heparin should be avoided in patients with potential VITT, unless heparin-induced thrombocytopenia testing is negative. Non-heparin anticoagulants and high-dose intravenous immune globulin should be considered in treatment of patients with VITT. Consultation with hematology specialists is strongly recommended. Both of the vaccines contain replication-incompetent adenoviral vectors (human [Ad26.COV2. S] for J&J and chimpanzee [ChAdOx1] for AstraZeneca) that encode the spike glycoprotein of SARS-CoV-2, the virus that causes COVID-19. Source: https://emergency.cdc.gov/; https://www.nejm.org/
