CD34 and COVID-19: We observed a scant quantity of non-organized endothelial cells in all thrombi, without differences between COVID-19 and control groups (respectively, median CD34+ area over total thrombus area = 0.23%, [IQR 0.12–0.71] vs. 0.37%, [IQR 0.10–0.95], p = 0.86) (Fig. 1B).