IL6 and COVID-19: Convalescent COVID-19 patients who did not undergo rehabilitation did not exhibit significant changes in ΔFMD (IL-6 ≥ 1.74 pg/mL: 0.70 (0.40)% vs. IL-6 < 1.74 pg/mL: 0.82 (1.65)%, p = 0.86) and percentage change in FMD (IL-6 ≥ 1.74 pg/mL: 16.5 (15.2)% vs. IL-6 < 1.74 pg/mL: 23.4 (39.7)%, p = 0.68) according to IL-6 levels.