Antigenic drift refers to the gradual accumulation of point mutations in viral genes encoding surface antigens, resulting in small but meaningful changes that allow viruses to evade host immune responses. This process generates new variants that are antigenically distinct from earlier strains.
Mechanism and drivers
RNA viruses such as influenza A and B replicate their genomes using RNA‑dependent RNA polymerases that lack proofreading activity, leading to a high mutation rate. When mutations occur in genes coding for exposed proteins like haemagglutinin and neuraminidase, they may alter epitopes recognized by neutralizing antibodies. Variants that escape existing immunity have a selective advantage and become dominant in the population. Antigenic drift is a continuous process driven by error‑prone replication and immune selection in individual hosts and at the population level. It differs from antigenic shift, which involves reassortment of gene segments and results in larger, abrupt antigenic changes. Drifting viruses may accumulate multiple amino‑acid substitutions over successive replication cycles, gradually altering antigenic sites while retaining overall protein function.
Examples and public health implications
Seasonal influenza epidemics illustrate the impact of antigenic drift. Circulating influenza A(H3N2), A(H1N1)pdm09 and B viruses undergo continual mutation; as antigenic drift accumulates, antibodies generated by previous infections or vaccinations become less effective. This necessitates periodic updates to influenza vaccine formulations to match prevailing strains and maintain vaccine effectiveness. Antigenic drift also occurs in other RNA viruses, such as noroviruses and coronaviruses, contributing to emergence of new variants with altered antigenicity. Continuous surveillance and antigenic characterization of circulating viruses allow public health agencies to anticipate drift and update vaccines and diagnostic reagents. Understanding antigenic drift underscores the importance of annual vaccination campaigns and ongoing research into broadly neutralizing antibodies and universal vaccines.
Antigenic drift is a gradual evolutionary process whereby small genetic changes in viral surface antigens help viruses escape immune recognition, driving seasonal epidemics and challenging vaccine design.
Related Terms: Antigenic shift, Mutation, Influenza virus, RNA virus, Vaccine