Title : Autoptic findings in VITT (Vaccine-induced Immune Thrombotic Thrombocytopenia alias Vaccine Induced Thrombosis with/without Thrombocytopenia)
Abstract:
Vaccine-induced Immune Thrombotic Thrombocytopenia (VITT), also known as vaccine-induced prothrombotic immune thrombocytopenia (VIPIT) or vaccine-associated thrombotic thrombocytopenia (VATT) or thrombosis with thrombocytopenia syndrome (TTS), is a rare potentially lethal blood clotting disorder first described after adenoviral vector-based vaccines against coronavirus disease 2019 (COVID-19). Both arterial and venous thrombosis may occur, including unusual sites such as the cerebral venous sinus or splanchnic vein. Therefore, the vaccines’ package inserts have been updated about this risk, as well as that concerning with venous thromboembolism without thrombocytopenia or immune thrombocytopenia without thrombosis. The life-threatening trigger of these post- vaccinal adverse events has been identified in the production of pathological platelet- activating antibodies against platelet factor 4 (PF4). By definition, the gold-standard criteria which must all be met for a definitive diagnosis of VITT are: anti-COVID-19 vaccine 4 to 42 days prior to symptom onset; any venous or arterial thrombosis (often cerebral or abdominal); thrombocytopenia (platelet count <150×103/mm3); positive PF4 heparin-induced thrombocytopenia (HIT) enzyme-linked immunosorbent assay (ELISA); (V) markedly elevated D-dimer (>4 times upper limit of normal). Besides adenoviral vector-based vaccines, there are also those exploiting a modified messenger ribonucleic acid (modRNA) technology, deem free from thrombotic complications. Indeed, my research group has investigated in depth a three-case series of thrombotic deaths in patients over fifty with comorbidities temporally after modRNA COVID-19 vaccination, all without thrombocytopenia. In light of these new acquisitions, a more appropriate rendering of the acronym VITT appears to be Vaccine Induced Thrombosis with/without Thrombocytopenia. Although remote in the face of millions of administered doses, clinicians should be aware of the possible thrombotic risk also after modRNA COVID-19 vaccines, in order to avoid a misdiagnosis with potentially fatal consequences.
