IL15 and COVID-19: However, when stratified according to sex (Table 4), levels of 25(OH)D showed a significant positive correlation with EFG (R = 0.39, p < 0.05) and IL-15 (R = 0.39, p < 0.05), and a borderline significant association with IFNγ (R = 0.33, p = 0.06) in male patients with COVID-19.