Abstract
Infectious bronchitis virus (IBV) remains a major pathogen in global poultry production due to its extensive genetic diversity and rapid evolutionary capacity. Antigenic diversification driven by mutation, homologous recombination, and sustained immune selection pressure complicates long-term control and reduces vaccine effectiveness. Increasing evidence suggests that IBV evolution is largely driven by the selective expansion of pre-existing variants under changing ecological and immunological conditions, rather than by the de novo emergence of novel lineages. South Korea provides a valuable model for understanding these processes within intensive poultry systems characterized by high host density, extensive farm connectivity, widespread vaccination, and long-term molecular surveillance. Since its first isolation in 1986, IBV in Korea has undergone repeated cycles of lineage emergence, diversification, and replacement, culminating in the predominance of nephropathogenic GI-19 viruses, including KM91 and QX-like variants. Persistent co-circulation of multiple lineages, together with frequent recombination and regional viral introduction, has shaped a highly dynamic viral population. Within this environment, vaccination plays a central yet paradoxical role. While essential for disease control, widespread vaccination imposes continuous immune selection pressure and may contribute to co-circulation of vaccine-derived and field strains, facilitating recombination and the emergence of immune escape variants. These processes drive lineage turnover and antigenic mismatch between circulating viruses and vaccine strains, forming a vaccination-driven evolutionary cycle. This review integrates global IBV diversity with insights from the Korean system to propose an evolution-centered framework in which viral genetic plasticity, host population dynamics, and vaccination practices interact. These findings have important implications for optimizing vaccination strategies and provide broader insights into the evolutionary dynamics of rapidly evolving RNA viruses under sustained immune pressure.