Double proline- substituted porcine epidemic diarrhea virus full-length spike mRNA vaccine confers enhanced immunogenicity and protective efficacy compared to conventional inactivated vaccine.

Porcine epidemic diarrhea virus (PEDV) is a highly contagious pathogen causing near 100% mortality in neonatal piglets, posing a persistent threat to the global swine industry. In this study, we isolated a PEDV strain, 23GXNN-1 (genotype G2c), from an outbreak in Guangxi, China. Two mRNA vaccine candidates were developed: one encoding the wild-type spike (S) protein S-WT and another incorporating proline-stabilized mutations (S-2P, I1076P/L1077P). Evaluations in HEK293T cells and animal models (BALB/c mice, sows, and piglets) revealed that the S-2P LNP-mRNA vaccine induced superior immunogenicity compared to S-WT, generating robust humoral immunity (elevated IgG/IgA titers and neutralizing antibodies) and enhanced cellular immune responses. Notably, maternal immunization with S-2P conferred 100% survival in piglets challenged with virulent PEDV G2c via efficient passive transfer of antibodies through colostrum, outperforming commercial inactivated vaccines. While vaccines provide limited protection to gut microbiota diversity and intestinal barrier integrity during infection, maternally derived antibodies effectively reduce disease severity. This study not only identifies S-2P as a promising candidate for PEDV control, but also underscores the crucial role of maternal immunity in neonatal protection, advancing mRNA-based strategies against enteric coronaviruses.