A worldwide anti-SARS-CoV-2 immunization campaign commenced at the end of 2020 using different vaccines that induce the production of an immunological response against the viral spike protein (Sp). To this aim, two different strategies are used: the first takes advantage of S-encoding mRNA carried inside the cells by lipid nanoparticles (BNT162B2, Pfizer-BioNTech; mRNA-1273, Moderna), while the other uses engineered adenoviruses (ChAdOx1 nCov-19, AstraZeneca; Ad.26.COV2.S, Johnson & Johnson), whose genes coding for replication have been disabled and replaced with others encoding the Sp. Although all these preparations can cause transient flu-like symptoms, adenovirus-based vaccines have been associated with extremely rare occurrence (<1 case/100,000 doses) of a syndrome resembling heparininduced thrombocytopenia (HIT), appearing 7–14 days after the injection and whose main features are the reduction of the platelet count and the formation of venous thrombi in both common and uncommon sites, including the cerebral venous sinuses (CVS) and portal system [1, 2]. A cause–effect
relationship with the vaccine has been hypothesized by some authors, who described this condition as vaccine-induced thrombotic thrombocytopenia (VITT) [3].
