A recent published review recommended a definite diagnosis upon meeting all of five criteria: (i) onset of symptoms 5–30 days post-COVID-19 vaccine (or up to 42 days if isolated DVT/PE), (ii) documented thrombosis or severe and persistent headache, (iii) thrombocytopenia (platelet count < 150,000/μL), (iv) D-dimer > 4000 FEU (and >8× ULN) and (v) positive anti-PF4/heparin IgG ELISA assay [30]. This evidence concerns the gene PF4 and Thrombocytopenia.