CD79A and COVID-19: The lack of a robust anti-RBD IgA response in breast milk and blood of vaccinated women can be attributed to the intramuscular route of administration of the mRNA vaccines.23 In addition, class switching to IgG occurs very quickly after COVID-19 vaccination24,25 in the absence of prior exposure, which explains why we did not detect RBD-reactive IgA in most milk samples.