Our results confirm that the parenteral mRNA anti-COVID-19 BNT162b2 vaccine is able to generate a strong systemic immune response as documented by high levels of specific IgA and IgG in the serum of vaccinated children; on the other hand, SARS-CoV-2 infection is associated to the presence of RBD-specific IgA2 in the saliva. The gene discussed is CD79A; the disease is COVID-19.