No cross-reactivity was found in the serum collected from patients uninfected with SARS-CoV-2 but diagnosed with hepatitis B (HB, n = 30), hepatitis C (HC, n = 30), or HIV infection (n = 30) detected by SARS-CoV-2 NP IgA ELISA. The gene discussed is CD79A; the disease is hepatitis B virus infection.