Platelet count and platelet activation induced by an mRNA COVID-19 vaccine-boosted Ad26.COV2.S-associated VITT patient. Patient platelet count (red circles) and results of the PF4-dependent PEA (blue circles) are displayed on the left and right y-axes, respectively. Administration of a booster dose of mRNA BNT162b2 vaccine is represented by the vertical dashed line. Time (in days) relative to booster vaccination is shown on the x-axis.