A homologous NADC34-like PRRSV-2 inactivated vaccine partially modulates pulmonary viral load and pathological lesions under controlled challenge conditions

Abstract

Background Porcine reproductive and respiratory syndrome virus (PRRSV) continues to cause substantial economic losses in the global swine industry, largely due to its rapid genetic evolution and capacity for immune evasion. Lineage 1 NADC34-like variants have become increasingly prevalent in East Asia, raising concerns about the effectiveness of existing vaccines against these emerging strains. Methods Herein, the effects of an inactivated NADC34-like vaccine strain derived from a contemporary Korean isolate were evaluated under homologous experimental challenge conditions. The vaccine antigen was prepared at a high titer (108 TCID50/dose), formulated with different adjuvants, including Carbopol/squalene-based formulations, and administered to 3-week-old pigs, followed by an intranasal challenge with a homologous NADC34-like strain. Clinical parameters, blood and tissue viral loads, humoral and cellular immune responses, and pulmonary pathology were assessed. Results Vaccinated pigs, particularly those receiving Carbopol/squalene-based formulations, exhibited reduced body temperature and lung viral loads, and lower microscopic interstitial pneumonia scores compared with nonvaccinated controls. However, no consistent or statistically significant reduction in systemic viral kinetics was observed across the vaccinated groups. Discussion These findings indicate that homologous inactivated vaccination does not achieve complete systemic viral suppression but its efficacy is limited to clinical mitigation and the reduction of pulmonary pathological outcomes. The dissociation between systemic viral load and pulmonary pathology highlights the complexity of vaccine evaluation in PRRSV infection. Nevertheless, the alleviation of body temperature, body weight, and lung lesions is of great significance in terms of protective potential against PRRS, a wasting disease, conferred by the inactivated vaccine.