Evaluation of the Prevention and Control Efficacy of Different Immunization Regimens Against Porcine Epidemic Diarrhea Virus.

Porcine epidemic diarrhea virus (PEDV) is an infectious pathogen that induces severe injury to the small intestinal epithelium of pigs. Pigs of all ages are susceptible to infection, which typically presents with watery diarrhea as the main clinical manifestation. In neonatal piglets, PEDV infection results in nearly 100% morbidity and mortality rates exceeding 80%. Therefore, selecting an appropriate immunization regimen for pregnant sows is particularly critical, as effective maternal vaccination enables the transfer of robust passive immunity to neonatal piglets, thereby protecting them against PEDV infection. In this study, three vaccination regimens (inactivated vaccine [IV] + IV, attenuated live vaccine [AV] + IV, and mRNA vaccine [MV] + MV) were used to immunize pregnant sows, and the passive immune protection conferred to neonatal piglets was subsequently evaluated. The results showed that piglets in the control group failed to acquire passive immune protection, with all piglets (5/5) developing diarrhea after challenge. The AV + IV regimen induced strong cellular immune responses and moderate humoral immunity, resulting in complete passive protection of piglets (5/5) following challenge, with only low levels of PEDV RNA detected in rectal swabs, which persisted for no more than 7 days. The IV + IV regimen elicited optimal humoral immune response but the weakest cellular immunity, whereas the MV + MV regimen induced moderate levels of both humoral and cellular immunity; piglets in both groups achieved partial passive protection (4/5), and relatively higher PEDV RNA loads, although still lower than those observed in the control group, were persistently detected in feces for up to 14 days. Collectively, the comparative analysis of passive immune protection conferred by the three immunization regimens indicated that the AV + IV strategy achieved superior protective efficacy, yielding superior outcomes compared with the MV + MV and IV + IV regimens. As MVs represent a novel and rapidly evolving platform for veterinary biologics, further technological innovation and systematic optimization are likely to enhance their immunogenicity and corresponding protective potency in subsequent studies.