Background: Protecting newborn piglets through maternal immunity

An mRNA vaccine candidate against porcine epidemic diarrhea virus (PEDV), incorporating proline substitutions in the spike protein, showed preclinical protection of newborn piglets through maternal immunity. The researchers reported 100% survival after a highly virulent PEDV G2c challenge in piglets that received antibodies in colostrum from sows vaccinated with S-2P. They noted, however, that protection of the gut microbiota and intestinal barrier was limited.

PEDV is a highly contagious pathogen that can cause mortality approaching 100% in newborn piglets. The researchers studied strain 23GXNN-1, isolated during an outbreak in Guangxi, China, which belongs to genotype G2c. The study focused on differences in immune responses resulting from vaccine antigen design and on piglet protection when antibodies formed in the sow were transferred through colostrum.

Key findings: Immune responses and survival with the proline-substituted candidate

The researchers developed two mRNA vaccine candidates: S-WT, encoding the wild-type spike protein, and S-2P, incorporating proline substitutions at two positions. The substitutions in S-2P are designated I1076P/L1077P, replacing the amino acids at those positions with proline.

Evaluation was conducted in HEK293T cells, BALB/c mice, sows, and piglets. The S-2P mRNA vaccine formulated in lipid nanoparticles (LNPs) showed greater immunogenicity—the ability to elicit an immune response—than S-WT. According to the abstract, immunoglobulin G (IgG) and immunoglobulin A (IgA) antibody titers and neutralizing antibody responses increased, and cellular immune responses were also enhanced. However, the abstract does not provide the magnitude of these increases or statistical values, making it difficult to quantify the differences. It also provides no structural analysis directly showing how stably the antigen maintained its prefusion structure.

In the maternal vaccination experiment, antibodies induced by S-2P were transferred through colostrum, and 100% survival was reported among piglets challenged with highly virulent PEDV G2c. The researchers described this protection as superior to that of a commercial inactivated vaccine. However, the abstract alone does not establish the number of piglets, control-group survival rate, vaccine dose and schedule, or observation period after challenge. The 100% figure reflects survival observed in that experiment; it does not mean complete protection under all husbandry conditions.

Implications and outlook: Survival benefits and intestinal barrier protection require separate assessment

These findings support enhancing immune responses in sows and transferring antibodies through colostrum as a candidate strategy for reducing the impact of PEDV in newborn piglets. The comparison of S-2P and S-WT also showed differences in immune responses associated with antigen design. More data are needed to determine in detail how these differences relate to protection in piglets.

The scope of protection also has limits. The abstract explicitly states that effects on preserving gut microbiota diversity and intestinal barrier integrity during infection were limited. This is why the finding that maternally derived antibodies reduced disease severity and contributed to survival should not be extended to mean that intestinal damage or microbiota disruption was fully prevented.

This study is a preclinical evaluation in cells and animals. The available information is insufficient to conclude that the vaccine's safety has been characterized in detail or that its effectiveness on farms has been established. Further evaluation should examine intestinal function and recovery as well as survival, and assess vaccination conditions and duration of protection. The paper appeared in volume 85 of Vaccine; the bibliographic record lists July 2026 as its publication month. The key findings and limitations can be found in the paper abstract indexed by Europe PMC.