Quadrivalent influenza virus hemagglutinin (HA) (HA)

Hemagglutinin (HA) is the primary surface glycoprotein of the influenza virus and is essential for the initiation of infection (UniProt, 2024). It mediates the binding of the virus to sialic acid receptors on host cell membranes and facilitates the subsequent fusion of the viral envelope with the endosomal membrane (StatPearls, 2023). The target refers to the quadrivalent composition used in modern influenza vaccines, which includes antigens from two influenza A subtypes (H1N1 and H3N2) and two influenza B lineages (Victoria and Yamagata) (CDC, 2023). These antigens are designed to elicit a protective immune response by inducing the production of neutralizing antibodies that primarily target the receptor-binding site on the HA globular head (WHO, 2024). Because influenza viruses undergo continuous antigenic drift, the specific HA sequences included in vaccines are updated annually to match circulating strains. Beyond vaccines, HA is a target for small-molecule inhibitors like umifenovir, which prevents viral entry by blocking the fusion process. Research is also ongoing into universal influenza vaccines that target the more conserved stem region of the HA protein to provide broader protection against multiple strains.

Other names

Influenza virus hemagglutinin antigens from four seasonal strainsQuadrivalent influenza vaccine antigensSeasonal influenza HA antigensInfluenza hemagglutinin

Vaccines containing these antigens induce the production of neutralizing antibodies that bind to the hemagglutinin protein, thereby blocking viral attachment to host cells and preventing infection (CDC, 2023). Antiviral drugs like umifenovir interact with hemagglutinin to inhibit the conformational changes required for membrane fusion (StatPearls, 2023).