Influenza hemagglutinin (HA) (HA)

Influenza hemagglutinin (HA) is the primary surface glycoprotein of the influenza virus and serves as the essential mediator for viral entry into host cells (UniProt P03437). It functions by binding to sialic acid receptors on the surface of target respiratory epithelial cells, followed by a pH-dependent conformational change that triggers the fusion of the viral envelope with the host endosomal membrane (PubMed: 29439209). As the dominant antigen on the viral surface, HA is the principal target of the protective immune response, making it the central component of seasonal and pandemic influenza vaccines (CDC, 2023). Vaccine strains are selected annually by the World Health Organization to match the HA sequences of circulating viruses, though the protein's high rate of mutation, known as antigenic drift, necessitates frequent updates to vaccine formulations (WHO, 2024). Beyond vaccines, HA is a target for antiviral development, including fusion inhibitors like Umifenovir and broadly neutralizing antibodies that aim to provide cross-strain protection by targeting conserved regions of the protein (PubMed: 30833457).

Other names

HemagglutininHaemagglutininHA proteinInfluenza A virus hemagglutininInfluenza B virus hemagglutininH1H3Viral surface glycoprotein

Vaccines containing or expressing hemagglutinin proteins induce the production of neutralizing antibodies that bind to the HA globular head, thereby blocking the virus from attaching to host sialic acid receptors (PubMed: 26912552). Antiviral agents like Umifenovir target the HA stem region to inhibit the pH-induced conformational changes required for the fusion of the viral envelope with the host cell membrane (PubMed: 30833457).