Antigenic drift and shift are distinct biological processes that alter viral antigenic properties, primarily described in segmented RNA viruses such as influenza. Antigenic drift is a continuous, gradual process driven by error-prone viral replication, leading to accumulation of point mutations in genes encoding surface proteins (e.g., hemagglutinin, neuraminidase), which incrementally modifies epitopes and enables immune escape. Antigenic shift is a discontinuous, abrupt process resulting from reassortment of genome segments during co-infection of a host cell by different viral strains, generating novel antigenic combinations and potentially new subtypes with limited population immunity. Both processes critically influence viral evolution, host range, and epidemic or pandemic potential.
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