Antigenic drift evaluation

Antigenic drift evaluation is a critical approach for monitoring genetic and antigenic changes in viral surface proteins, particularly hemagglutinin (HA), that may impact immune recognition and vaccine effectiveness. This assessment is commonly performed by comparing antibody reactivity against contemporary circulating strains and reference vaccine strains using serological assays such as HAI and virus neutralization tests. By measuring reductions in antibody titers to drifted strains relative to homologous strains, antigenic drift analyses enable the identification of antigenic variants with decreased susceptibility to pre‑existing immunity. These studies are essential for influenza surveillance programs and inform vaccine strain selection decisions coordinated by international regulatory and public health authorities, including the World Health Organization (WHO) and the European Medicines Agency (EMA).