Shultz et al. analyzed five patients who presented with venous thrombosis and thrombocytopenia 7 to 10 days after receiving the first dose of the ChAdOx1 nCoV-19 vaccine and found that all the patients had high levels of antibodies to platelet factor 4 (PF4)–polyanion complexes35. Here, PF4 is linked to Thrombocytopenia.