COVID-19, vaccines, and thrombotic events

COVID-19, a deadly pandemic that has affected millions of people worldwide, is also associated with car-diovascular complications, such as venous and arterial thromboembolic events. The viral spike protein, in fact, may promote the release of prothrombotic and inflammatory mediators. Vaccines, coding for the spike protein, are the primary measure for preventing COVID-19. However, some unexpected thrombotic events at unusual sites, most frequently the cerebral venous and splanchnic districts, with associated thrombocyto-penia, have emerged in subjects who received adenovirus-based vaccines, especially in fertile women. This clinical entity has been rapidly recognized as a new syndrome, named vaccine-induced immune thrombotic thrombocytopenia, probably caused by cross-reacting antiplatelet factor 4 antibodies activating platelets. This prompted the regulatory agencies of various countries to restrict the use of adenovirus-based vaccines to specific age groups. The prevailing opinion of most experts, however, is that the risk of developing COVID-19 disease, including thrombosis, clearly outweighs this potential extremely low risk. This paper aims at providing a comprehensive review of epidemiological issues, clinical data and pathoge-netic hypotheses of thrombosis linked to both COVID-19 and its vaccines, helping cardiologists to offer an up-to-date and evidence-based counseling to their often-alarmed patients with acute or chronic coronary syndromes.