Patients were classified as having primary antibody deficiency (PAD), combined immunodeficiency, or innate immune defects.<h4>Results</h4>Receptor-binding domain (RBD)-specific IgG levels were comparable between infected children and vaccinated adults; however, PAD patients exhibited the weakest systemic and mucosal humoral responses, with markedly reduced salivary IgA. Here, CD79A is linked to severe combined immunodeficiency.