PF4 and COVID-19: Regarding the role of the spike protein in platelet activation and VITT, according to the latest results published23, the spike protein present in the COVID-19 vaccines is not considered to be the main driver of the immune response at the start of the prothrombotic cascade as VITT patients experiencing COVID-19 after vaccination do not show a boosted anti-PF4 antibody response nor a relapse of VITT.