Molecular surveillance of GI-19 lineage infectious bronchitis virus in China: divergent evolution and efficacy assessment of QXL87 vaccine against heterologous clades

This study underscored the substantial genetic divergence within the dominant GI-19 lineage of IBV, resulting in the emergence of multiple clades. Despite this, the QXL87 vaccine remained effective for preventing GI-19 lineage IBV infection although the protection rates differed among different clades. However, we must acknowledge that in cross-protection trials, ciliary motility scores for clade 1 and clade 3 marginally dropped below 80% according to a more accurate calculation method published. Consequently, ongoing surveillance for mutations of circulating IBV strains remains critical. In case the antigenic drift compromises vaccine efficacy, timely updating vaccine strains or immunization strategies involving multiple vaccine candidates should be prioritized to ensure sustained protection.