Protective vaccines elicit high-affinity, neutralizing antibodies by selection of somatically hypermutated B cell antigen receptors (BCR) on immune complexes (ICs). This implicates Fc-Fc receptor (FcR) interactions in affinity maturation, which, in turn, are determined by IgG subclass and Fc glycan composition within ICs. Trivalent influenza virus vaccination elicited regulation of anti-hemagglutinin (HA) IgG subclass and Fc glycans, with abundance of sialylated Fc glycans (sFc) predicting quality of vaccine response. We show that sFcs drive BCR affinity selection by binding the Type-II FcR CD23, thus upregulating the inhibitory FcγRIIB on activated B cells. This elevates the threshold requirement for BCR signaling, resulting in B cell selection for higher affinity BCR. Immunization with sFc HA ICs elicited protective, high-affinity IgGs against the conserved stalk of the HA. These results reveal a novel, endogenous pathway for affinity maturation that can be exploited for eliciting high-affinity, broadly neutralizing antibodies through immunization with sialylated immune complexes. Display omitted •Dynamic changes in Fc glycan composition following influenza vaccination•Sialylated Fc glycan abundance on anti-HA IgG predicts vaccine response•Sialylated Fc immune complexes engage CD23 and BCR to modulate affinity maturation•IgGs elicited by sialylated Fc immune complexes protect broadly against H1 viruses The glycan composition of the Fc region of anti-influenza antibodies changes following vaccination, with sialylated Fc glycan abundance predicting the quality of the vaccine response and production of high-affinity antibodies against the conserved stalk domain of the influenza HA.