IGHA1 and influenza: Comparing pre- and postvaccination antibody levels in a subset of the 2018 vaccine cohort, we detected high increases for IgG1, IgG3, IgA1, FcγRIIa, and FcγRIIIa MFIs toward almost all influenza antigens postvaccination (Fig. 5A and SI Appendix, Fig. S5A).