Efficacy of dual administration vaccine of recombinant Newcastle disease virus expressing clade 2.3.4.4b H5 hemagglutinin against H5N1 highly pathogenic avian influenza and viscerotropic Velogenic Newcastle disease virus in broilers.

The widespread and endemic nature of recent highly pathogenic avian influenza virus H5N1 clade 2.3.4.4b outbreaks has driven increased vaccine demand. In this study, we used a Newcastle disease virus (NDV) vector expressing clade 2.3.4.4b H5 hemagglutinin (rK148/22-H5) to evaluate the efficacy of a single-dose vaccine administered via dual routes. We vaccinated 1-day-old broilers and randomly assigned them to HPAIV and viscerotropic velogenic NDV (vvNDV) challenges every 10 days. In the control group, maternal NDV antibodies waned by 20 days of age, whereas the antibody levels were sustained in the vaccinated group. Antibodies against HPAIV were first detected at 20 days post vaccination (dpv). Starting at 20 dpv, protection rates exceeded 70% and 90% against vvNDV and HPAIV challenges, respectively. Notably, at 30 dpv, no virus shedding was detected in the oropharyngeal and cloacal tissues following highly pathogenic avian influenza challenge. The rK148/22-H5 vaccine administered via the dual route is a promising candidate for single-dose vaccination to effectively protect young chicks against HPAIV and vvNDV.