Study identifies adenovirus core protein VII (pVII) as the triggering antigen of VITT, a rare condition with thrombosis and thrombocytopenia following adenovirus vaccines such as AstraZeneca ChAdOx1 nCoV-19 and Johnson & Johnson Ad26.COV2.S[1][2][3]. VITT occurs 5 to 30 days after the first dose, with an incidence of approximately 1 to 15 cases per million doses, higher in young women (AstraZeneca 1/50,000–100,000)[1]. The pVII protein exhibits molecular mimicry with PF4, leading to the generation of pathogenic antibodies against PF4 through somatic hypermutation in B-cells[1][2][3]. These antibodies strongly activate platelets in the presence of PF4 independently of heparin[1]. A genetic risk factor is associated with the IGLV3.2102 antibody gene, more often in people of European descent[3][4]. VITT is not only caused by vaccination, but can also occur after natural adenovirus infections[2]. Mortality was originally 20–30%, now lower with treatments such as argatroban and IVIG; clots often affect the brain (50% cerebral venous)[1]. The results allow modification of pVII in vaccines to eliminate the risk[3][4].