Few type-specific antibodies that recognize drifted epitopes are made during post-vaccination exposures to SARS-CoV-2 variants1–12, perhaps due to suppression by previous immunity. We compared type-specific B cell responses in unvaccinated and vaccinated individuals with Delta and Omicron BA.1 SARS-CoV-2 variant infections. For both Delta, which is antigenically similar to the vaccine strain, and the more distant BA.1 variant, neutralizing antibodies were greater in post-vaccination variant infections than in primary variant infections. Delta type-specific memory B cells were reduced in post-vaccination Delta infections relative to primary variant infections. Yet some drifted epitopes in the Delta variant elicited minimal responses even in primary infections. For BA.1 infections, type-specific antibodies and memory B cells were mostly undetectable, irrespective of previous immunity. Thus, poor intrinsic antigenicity of drifted epitopes in Delta and BA.1 infections superseded the impact of previous immunity. Enhancing the immunogenicity of vaccine antigens may promote type-specific responses.
