HLA-DRB1 and viral infectious disease: In fact, the presence of ≥ 3 mismatches in HLA class I was associated with a significantly higher viral infection incidence after being adjusted by HLA-DRB1 mismatch and other confounding factors (Table 2 and Fig. 2A) (HR 2.38 [1.09–5.17], p = 0.02).