Persistently high platelet factor 4 levels in an adolescent with recurrent late thrombotic complications after SARS-CoV-2 mRNA vaccination: A case report

Abstract

Background Thrombosis after severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) vaccination is a serious complication for patients with a thrombophilic predisposition. Factors that predict the risk of post-vaccination thrombosis should be explored. We report a case in which a patient with pediatric antiphospholipid syndrome (APS) developed deep vein thrombosis (DVT) six months after receiving a second dose of the BNT162b2 vaccine. Case presentation: A 17-year-old girl with no family history of thrombophilia developed DVT at six years of age. The thrombus was found in the right common iliac vein and the inferior vena cava, with concomitant left pulmonary infarction. After treatment with warfarin, the pulmonary infarction was resolved, but the thrombus became organized and persisted for the next 11 years. The patient was treated with anticoagulants for six years after DVT onset, with subsequent cessation of treatment for five years without thrombosis recurrence. She received the BNT162b2 vaccine at 17 years of age, one week before a routine outpatient visit. Elevation of platelet factor 4 level was detected 14 days after the first vaccination and remained for five months after that, but without thrombotic symptoms. A second dose of the BNT162b2 vaccine was administered; six months later, the DVT in the right common iliac vein recurred and was treated with a direct oral anticoagulant. Conclusions The BNT162b2 vaccine exacerbated her antiphospholipid antibody syndrome by activating the coagulation system, thereby exacerbating her thrombosis. Platelet factor 4 may be a useful indicator of the coagulation system. The persistence of high platelet factor 4 levels after vaccination suggests that the vaccine caused DVT by exacerbating the patient’s APS. After vaccination of patients with a predisposition to thrombosis, coagulation status and platelet activation markers should be monitored to prevent the development of DVT.