Significant predictive factors for moderate to severe Omicron infection included older age (p < .0001), cGVHD (p = .0195), concurrent bacterial infection (p < .0001), low absolute lymphocyte count (p = .026), low CD4/CD8 ratio (p = .0091), high CRP (p < .0001), high serum ferritin (p = .0023), high D‐dimer (p < .0001), low CD4 absolute count (p = .0057), and low B‐cell absolute count (p = .0154). This evidence concerns the gene CD4 and bacterial infectious disease.