A chimeric PRRSV vaccine with dual Nsp2 deletions elicits cross-lineage protection against heterologous challenge.

Porcine reproductive and respiratory syndrome virus (PRRSV) remains a major threat to swine health worldwide. In China, the co-circulation of lineage 8.7 (HP-PRRSV-like) and lineage 1.8 (NADC30-like) strains poses a particular challenge due to the limited cross-protection provided by current vaccines. To broaden immunity, we engineered a chimeric virus, rFX1701, based on a lineage 8.7 backbone but carrying an additional 131-aa deletion in Nsp2 characteristic of lineage 1.8 strains, thereby creating a dual-deletion antigenic architecture. The rescued virus replicated efficiently in vitro and exhibited an attenuated phenotype in piglets, inducing low-level, transient viremia and no significant clinical signs. Vaccination with rFX1701 stimulated robust anti-PRRSV antibodies, cross-neutralizing activity against both lineages, and a balanced Th1/Th2 cytokine response. Under the conditions tested, rFX1701-vaccinated pigs showed no fever, clinical disease, or significant lung pathology after challenge, and effectively cleared the challenge virus. In contrast, a commercial HP-PRRSV-based modified live virus (MLV) vaccine failed to protect against the lineage 1.8 challenge. These results demonstrate that the chimeric virus rFX1701, engineered to present two lineage-specific deletions in Nsp2, was associated with protection against clinical disease following heterologous challenge in this proof-of-concept study. This design supports further evaluation as a candidate cross-lineage vaccine approach.