PF4 and autoimmune thrombocytopenic purpura: Vaccine-induced immune thrombocytopenia and thrombosis (VITT) is a new clinical entity first described after the administration of adenovirus-vectored COVID-19 vaccines including Ad26.COV2.S (Janssen, referred to hereafter as Ad26) and ChAdOx1 nCoV-19 (AstraZeneca, referred to hereafter as ChAdOx1), VITT is characterised by the onset of symptoms 5–30 days after COVID-19 vaccination, with thrombocytopenia, thrombosis, presence of anti-platelet factor 4 (PF4) antibodies, and grossly elevated D-dimer1.