A bivalent subunit vaccine elicits robust immune responses and neutralizing antibodies against genogroup 1b and 2b porcine epidemic diarrhea viruses

Porcine epidemic diarrhea virus (PEDV) is a member of the family Coronaviridae and genus Alphacoronavirus in the order Nidovirales. It causes porcine epidemic diarrhea (PED) which is characterized by diarrhea, vomiting, and dehydration in swine and is fatal in neonatal piglets with a mortality rate of up to 100%. It is highly contagious, thus resulting in mass epidemics that can have a significant impact on the swine industry. The emerging strains of PEDV are majorly divided into G1b (S-INDEL), and G2b (non-S-INDEL) genogroups based on the spike S1 protein and their virulence. The current vaccines target only one genogroup. In this study, we developed a novel bivalent subunit vaccine by generating a fusion protein of the S1 proteins of both genogroups. For immunogenicity evaluation, mice were intramuscularly immunized twice with the subunit vaccine formulated with three Montanide adjuvants: IMS 1313 VGN, Gel 02 PR, or ISA 61 VG. Results showed that all adjuvanted vaccines induced robust IgG and IgA responses against S1 proteins of both genogroups. IgG1 and IgG2a quantification showed IMS 1313 VGN and ISA 61 VG formulations elicited Th2-biased immune responses, whereas Gel 02 PR adjuvanted subunit vaccine induced balanced immune responses. More importantly, the formulated vaccines elicited neutralizing antibody titers against PEDV infections of both genogroups, with the ISA 61 VG group inducing neutralizing titers greater than 1:64. These pre-clinical results demonstrate that the bivalent subunit vaccine is a promising vaccine candidate against multiple PEDV genogroups that should be further tested in pig trials.