Influenza A and B hemagglutinin proteins (HA)

Hemagglutinin (HA) is the primary surface glycoprotein of influenza A and B viruses and serves as the principal target for seasonal influenza vaccines. It functions as a lectin that binds to sialic acid residues on the surface of host respiratory epithelial cells, initiating viral entry via endocytosis (UniProt, 2024). Following internalization, a pH-dependent conformational change in the HA2 subunit triggers the fusion of the viral envelope with the endosomal membrane, releasing the viral genome into the cytoplasm (PubMed, PMID: 22226115). Because the HA protein is subject to continuous antigenic drift, vaccine-matched seasonal strains are selected annually by the WHO to ensure that the antibodies elicited by vaccination effectively neutralize circulating viruses (CDC, 2024). Therapeutic strategies targeting HA include both the induction of active immunity through vaccines and the development of small-molecule inhibitors like umifenovir that block the protein's fusion capabilities (DrugBank, 2024). Effective targeting of HA is essential for reducing the global burden of seasonal influenza and preventing potential pandemics.

Other names

HemagglutininHAInfluenza virus hemagglutininH1H3HA1 subunitHA2 subunit

Induction of neutralizing antibodies that block viral attachment to host cells; inhibition of the pH-dependent conformational change required for membrane fusion.