Efficacy of an optimal vaccination strategy for H120 and NNA vaccines against the novel HX strain of the IBV GVI-1 genotype

The infectious bronchitis virus (IBV) causes significant economic losses to the global poultry industry. Recently, there has been a rapid spread of the GVI-1 lineage of IBV in Asia, particularly in China. However, to date there have been few studies that have assessed the immune protection efficacy of commonly used IB vaccines against the GVI-1 lineage strains. In this study, we evaluated the protective efficacy of two commonly used vaccines, H120 and NNA, against the GVI-1 lineage HX strain based on serological neutralization tests and animal challenge protection experiments. The protective efficacy of sera from chickens immunized using different vaccination strategies against the HX strain was evaluated using chicken embryos, with the results indicating that a combined vaccination strategy using H120 and NNA provided better antiviral effects in chicken embryos than those obtained using either of these two vaccines administered alone. In challenge protection experiments on chicks, we assessed clinical symptoms, viral loads in the trachea and kidneys, and histopathological damage levels. The results revealed that when administered alone, the H120 and NNA vaccines were unable to provide complete protection against HX strain infection, whereas the combined vaccination reduced the pathological damage caused by infection. Multiple bioinformatics analyses revealed significant differences in the nucleic acid and amino acid similarities between the GVI-1 lineage strain HX and the attenuated vaccine strains H120 and NNA, particularly in the S1 gene antigenic epitopes. Our findings in this study, in which we examined the differences in immune protection efficacy of two IB vaccines against a GVI-1 lineage strain, can provide a theoretical basis for optimizing vaccine design.