Efficacy of a Commercial PRRSV Vaccine on NADC34-Like PRRSV Challenge.

NADC34-like porcine reproductive and respiratory syndrome virus (PRRSV) has become endemic in some provinces of China and caused huge economic losses to local pig industry. The increased reports of NADC34-like PRRSV outbreaks in vaccinated pig herds suggest the limited protection of immunization with commercial vaccines. In this study, we evaluated a commercial PRRSV vaccine that has been widely used in China against the challenge of JS2021NADC34 PRRSV, a highly pathogenic Chinese NADC34-like strain isolated in 2021. The vaccinated pigs developed PRRSV-specific antibody responses, as shown by IDEXX ELISA results. After JS2021NADC34 PRRSV challenge, the vaccinated pigs had low level of viremia but suffered pathological lesions in lungs and lymphoid tissues. The viral antigens were also detected in the above tissues of the vaccinated pigs by immunohistochemistry staining. One out of five pigs in vaccinated group died at 13 days postchallenge. The above results suggested that the commercial PRRSV vaccine could not provide complete protection to the NADC34-like PRRSV infection.