Defining the Antigenic Topology and Prospective Binding Breadth of Vaccination-induced SARS-CoV-2 Neutralizing Antibodies

Abstract Antibodies that neutralize SARS-CoV-2 primarily target the viral spike glycoprotein, yet the breadth of these responses is continually challenged by viral evolution. While extensive structural studies have defined epitopes across the spike protein, how antibodies elicited by the initial mRNA vaccination campaigns perform against subsequently emerging variants remains an important question. Here, we structurally and functionally characterize a panel of early plasmablast-derived human monoclonal antibodies isolated following primary mRNA vaccination, targeting both the receptor-binding domain (RBD) and the N-terminal domain (NTD) of spike. Using cryo–electron microscopy, variant-binding analyses, and viral-fusion inhibition assays, we observe that antibodies directed against immunodominant regions of the RBD and NTD are highly potent but more frequently impacted by variant-associated mutations. In contrast, antibodies engaging a conserved hydrophobic pocket within the NTD exhibit broader reactivity and neutralize through distinct molecular mechanisms. Together, these findings extend prior structural studies of spike-directed antibodies by prospectively assessing the breadth of vaccine-elicited antibodies against later variants and identifying structural features associated with differential escape sensitivity. These results contribute to a growing understanding of how early vaccine-induced antibody repertoires relate to subsequent viral evolution. One sentence summary Antibody epitopes on SARS-CoV-2 spike determine prospective breadth and vulnerability to viral evolution.