Noppacharn Uaprasert,1,2 Ponlapat Rojnuckarin1,2

1 Division of Hematology, Department of Medicine, Faculty of Medicine, Chulalongkorn University and King Chulalongkorn Memorial Hospital
2 Research Unit in Translational Hematology, Faculty of Medicine, Chulalongkorn University and King Chulalongkorn Memorial Hospital

Abstract

Background: Vaccine-induced immune thrombotic thrombocytopenia (VITT) is a distinctive syndrome characterized by unusual site thrombosis accompanied by thrombocytopenia following adenoviral vector vaccines against severe acute respiratory syndrome coronavirus 2. Platelet-activating anti-platelet factor 4-dependent antibodies (anti-PF4 Abs) have been identified as pathogenic antibodies in almost all patients.
Objective: We proposed an immunological mechanism of VITT independent of anti-PF4 Abs.
Method: Case report.
Results: A 68-year-old Thai woman developed pulmonary embolism and deep vein thrombosis with thrombocytopenia one week after the second ChAdOx1 nCoV-19 vaccination with undetectable anti-PF4 Abs. The platelet count responded rapidly to intravenous immunoglobulin and steroids. Therefore, the high clinical suspicion is essential for early recognition and prompt management irrespective of anti-PF4 Ab results.
Conclusion: We hypothesize that platelet and endothelial activation following ChAdOx1 nCoV-19 vaccination may lead to generation of pathogenic antibodies which account for VITT independent of anti-PF4 Abs.
Key words: thromboembolism, platelet factor 4, vaccine, adenoviral vector, antibody