Abstract
Vaccine-induced immune thrombosis and thrombocytopenia (VITT) is classically associated with adenoviral vector vaccination. VITT is part of a wider group of diseases known as PF4-associated immunothrombosis with thrombocytopenia (PITT), which includes heparin-induced thrombocytopenia (HIT). PITT can also manifest in individuals without either proximate vaccine or heparin exposure, most notably following adenoviral infection. Although we are aware of reports of VITT following non-adenoviral vector vaccination, it is unclear whether those attributed to mRNA-based vaccination truly represent VITT, or whether they reflect the background incidence of spontaneous syndromes coupled with heightened awareness. This systematic review aimed to identify and collate cases of PITT that are related to non-adenoviral vector vaccines using wide search terms, then systematically assess the likelihood of VITT using recognized criteria. Of 42 included cases, only 5 met criteria for “definite” VITT; however, none were wholly convincing. VITT triggered by non-adenoviral vector vaccination, therefore, appears very rare or possibly non-existent.
