Background. Rapidly evolving RNA viruses, such as human norovirus, generate extraordinary sequence diversity, posing a significant challenge to vaccine design. This diversity, coupled with short-lasting natural immunity, leads to reinfection throughout one's lifetime. How reexposure shapes humoral immunity to future norovirus strains remains incompletely understood. Methods. We profiled the antibody responses following 2 community gastroenteritis outbreaks with GII.2 and GII.6 noroviruses in 1971. Using diverse virus-like particles (VLPs), enzyme-linked immunosorbent assay (ELISA), and carbohydrate-blocking assays (surrogate for neutralization), we examined the antibody response at acute and convalescent timepoints following GII.6 infection. Results. Convalescent sera displayed strong homologous blocking, demonstrating a 5-fold increase in GII.6 carbohydrate blockade over acute samples, and broad blocking of diverse archival and modern GII.6 noroviruses. Convalescent sera displayed limited carbohydrate blocking of heterotypic VLPs, despite high ELISA binding titers. Select individuals developed broad cross-genotype blockade, but this response was established before the second outbreak. Finally, we applied a novel competitive carbohydrate-blocking assay to demonstrate the epitope specificity and discrete compartments of the neutralizing response. Conclusions. Our data show that infection generates narrow, focused immunity directed toward the infecting genotype. We did detect broad cross-blocking in specific individuals, but these responses could be attributed to diverse, genotype-specific antibodies predating GII.6 infection. By profiling serum antibody binding and neutralization activity following 2 community gastroenteritis outbreaks, we found that diverse norovirus exposure failed to expand histo-blood group antigen-blocking antibody breadth and that the responses are genotype-specific, rather than broadly neutralizing.
