Two major antigenically heterogenous norovirus genogroups (GI and GII) commonly infect humans and are the leading cause of foodborne, viral gastrointestinal infections in adults.

We assessed B cell responses in participants in a double-blind, placebo-controlled, dose-escalation phase 1 study of the safety and immunogenicity of an intramuscular bivalent norovirus virus-like particle (VLP) vaccine. The vaccine contained a GI.1 VLP (Norwalk) and a consensus GII.4 VLP, representing the two major genotypes that cause human disease, and was administered on days 0 and 28 to healthy adults aged 18–49 years. Four separate cohorts received increasing doses of 5 μg, 15 μg, 50 μg, and 150 μg of each VLP adjuvanted in monophosphoryl lipid A and alum. PBMCs were analyzed for B cell activation and mucosal homing markers (flow cytometry) and VLP-specific and total IgG and IgA Ab-secreting cells (ASCs); and serum titers of VLP-specific IgG, IgA, and Pan-Ig were determined.

The vaccine elicited CD27+ CD38+ plasmablasts and high frequencies of ASCs specific for both VLP antigens in the peripheral blood at 7 days after the first dose. The plasmablasts exhibited a mucosal-homing phenotype and included a high proportion of IgA ASCs. Serum antibodies increased as early as 7 days after the first immunization.

The data suggest that a single dose of the IM bivalent norovirus vaccine is effective in activating pre-existing B cell memory. The rapid B cell response and the mucosal homing phenotype of induced ASCs are consistent with anamnestic responses in subjects primed by prior oral norovirus infection.

This study is registered at ClinicalTrials.gov Identifier NCT01609257.