CD8A and COVID-19: As depicted in Tables 3 and 4, the Spearman correlation analysis results revealed that the presence of diabetes was positively correlated with age (r = 0.346), hs-CRP (r = 0.556), LDH (r = 0.635), IL-6 (r = 0.703), CD8+ (r = 0.332), severity of COVID-19 (r = 0.318) and negatively correlated with CD3+ (r = −0.638), CD4+ (r = −0.351), CD4+/CD8+ (r = −0.652), and the presence of secondary hyperglycemia was positively associated with IL-6 (r = 0.411) and inversely correlated with CD3+ (r = −0.388) and CD4+ (r = −0.391).