Sequence-Aware Antigenic Alignment and SRID Potency Interpretation in Influenza Vaccines.

Single radial immunodiffusion (SRID) remains the standard potency assay for seasonal influenza vaccines worldwide. Because SRID depends on antigen-antibody recognition, hemagglutinin (HA) sequence variation can influence potency interpretation through its effects on antigenic alignment among vaccine antigens and reference reagents. This review examines the relationship between viral propagation, antigenic fidelity, and reference reagent alignment, and proposes sequence-aware antigenic alignment as a conceptual framework linking HA sequence variation to SRID potency interpretation and harmonization.