Greinacher et al. and Lee et al. reported thrombocytopenia in an adenovirus vector vaccine and mRNA vaccine recipients.154,164 A large number of platelet factor 4 (PF4) antibodies were presented in the patients, and the antibody heparin PF4 complex acted on platelet FC γ receptors, activating platelets and further producing procoagulant substances.154 Adenoviruses can bind to platelets and activate them.165,166 However, trace adenoviruses in vaccines injected one or two weeks before onset seem unlikely to cause platelet activation. This evidence concerns the gene PF4 and Thrombocytopenia.