A probable case of vaccine-induced immune thrombotic thrombocytopenia secondary to Pfizer Comirnaty COVID-19 vaccine

The accelerated development of various vaccines against COVID-19 was a global effort to curb the COVID-19 pandemic. As a result, several unique vaccine-related adverse events were observed. Vaccine-induced immune thrombotic thrombocytopenia (VITT) has been recognised as a clinically distinct entity with a predisposition for thrombosis at unusual sites with laboratory features of consumptive coagulopathy in addition to anti-PF4 assay seropositivity. The majority of cases reported were associated with adenoviral-based vectors such as ChAdOx1 nCoV-19 (Oxford-AstraZeneca) and Janssen Ad26.COV2.S (Johnson & Johnson). In our online search, we have not found any reports to date of VITT associated with Pfizer-BioNTech Comirnaty mRNA vaccine. We report a case of a previously healthy 76-year-old man who received his first-dose Pfizer Comirnaty vaccine on 11 October 2021 who developed left upper limb swelling on day 2 post-vaccination, which progressively worsened on day 4 post-vaccination. He was confirmed to have left axillary vein thrombosis on computer tomography arteriography/computed tomography venography of left upper limb on day 5 post-vaccination with new onset aphasia with unilateral limb weakness on day 8 post-vaccination. Magnetic resonance imaging/magnetic resonance angiography of the brain confirmed acute left middle cerebral artery thrombosis with infarction. Blood investigations showed thrombocytopenia, elevated D-dimer, hypofibrinogenemia in addition to his unusual sites of thrombosis involving both arterial and venous circulation. His IgG ELISA assay for anti-PF4 antibody was positive.