Genotype considerations for virus-like particle-based bivalent norovirus vaccine composition.

Norovirus (NoV) genogroup I (GI) and GII are responsible for most human infections with NoV. Because of the high genetic variability of NoV, natural infection does not induce sufficient protective immunity to different genotypes or to variants of the same genotype and there is little or no cross-protection against different genogroups. NoV-derived virus-like particles (VLPs) are promising vaccine candidates that induce high levels of NoV-specific humoral and cellular immune responses. It is believed that a bivalent NoV vaccine consisting of a representative VLP from GI and GII is a minimum requirement for an effective vaccine. Here, we compared the abilities of monovalent immunizations with NoV GI.1-2001, GI.3-2002, GII.4-1999, and GII.4-2010 New Orleans VLPs to induce NoV type-specific and cross-reactive immune responses and protective blocking antibody responses in BALB/c mice. All of the VLPs induced comparable levels of type-specific serum IgG antibodies, as well as blocking antibodies to the VLPs used for immunization. However, the abilities of different VLP genotypes to induce cross-reactive IgG and cross-blocking antibodies varied remarkably. Our results confirm previous findings of a lack of cross-protective immune responses between GI and GII NoVs. These data support the rationale for including NoV GI.3 and GII.4-1999 VLPs in the bivalent vaccine formulation, which could be sufficient to induce protective immune responses across NoV genotypes in the two common genogroups in humans.