Quadrivalent influenza virus hemagglutinin (QIV HA)

Influenza virus hemagglutinin (HA) is the primary surface glycoprotein of the influenza virus and serves as the critical immunogen in seasonal vaccines (CDC, 2023). It functions by binding to sialic acid receptors on the surface of host respiratory epithelial cells, facilitating viral entry through endocytosis and subsequent membrane fusion (UniProt, 2024). In a quadrivalent vaccine formulation, HA antigens are derived from four distinct viral lineages: two influenza A subtypes (typically H1N1 and H3N2) and two influenza B lineages (Victoria and Yamagata) (WHO, 2024). These antigens are presented to the host immune system to stimulate the production of neutralizing antibodies, primarily targeting the globular head of the HA protein to prevent viral attachment (StatPearls, 2023). Because influenza viruses undergo frequent antigenic drift, the specific HA sequences included in vaccines are updated annually based on global surveillance (NIH, 2023). Beyond vaccines, HA is also a target for monoclonal antibodies and small-molecule fusion inhibitors designed to treat active infections (PubMed, 2022). The induction of high-affinity antibodies against the conserved stem region of HA is a major goal for the development of universal influenza vaccines (Nature, 2021).

Other names

Influenza hemagglutininHA antigenQuadrivalent influenza vaccine antigensH1N1, H3N2, B/Victoria, and B/Yamagata hemagglutininsSeasonal influenza vaccine immunogens

The mechanism involves the presentation of purified, recombinant, or inactivated hemagglutinin proteins to the immune system to elicit the production of neutralizing antibodies (IgG and IgA). These antibodies bind to the HA1 subunit (globular head) or the HA2 subunit (stem), sterically hindering the interaction between the virus and host cell sialic acid receptors, thereby neutralizing viral infectivity and preventing the fusion of the viral envelope with the endosomal membrane (CDC, 2023; PubMed, 2021).