CD79A and infection: Since all individuals within group A tested negative with a certified SARS-CoV-2 antibody test (Elecsys® Anti-SARS-CoV-2 assay Roche) and had no medical history of infection with SARS-CoV-2, other possibilities than SARS-CoV-2 exposure for the presence of the detected RBD-specific low-level IgG and IgA reactivities may be considered, among them cross-reactivity with other coronaviruses.