CD38 and COVID-19: We found that after 100,000 IU cholecalciferol supplementation, patients with COVID-19 had decreased frequencies of CD38++CD27 transitional and mature naive CD27−CD38+ B cells if compared to Group II (1.43% (0.79; 2.08) vs. 2.74% (1.43; 3.91), p = 0.006 and 57.57% (25.15; 66.82) vs. 67.03% (51.16; 74.71), p = 0.02, respectively).