Quadrivalent influenza hemagglutinin (HA)

Hemagglutinin (HA) is the primary surface glycoprotein of the influenza virus, serving as a critical mediator of viral entry into host cells. It functions by binding to sialic acid receptors on the surface of host respiratory epithelial cells and subsequently facilitating the fusion of the viral envelope with the endosomal membrane (UniProt, 2024). The "four strains" designation refers to the composition of quadrivalent influenza vaccines, which include HA antigens from two influenza A subtypes (H1N1 and H3N2) and two influenza B lineages (Victoria and Yamagata) (CDC, 2023). These antigens are the primary targets of the host immune response, specifically for the production of neutralizing antibodies that prevent infection (WHO, 2024). In addition to vaccines, HA is a target for antiviral drugs like Umifenovir, which inhibits the conformational changes required for membrane fusion (PubMed, 2017). The high rate of mutation in the HA gene, known as antigenic drift, necessitates the annual reformulation of these antigens to ensure vaccine efficacy against circulating seasonal strains (StatPearls, 2023).

Other names

Hemagglutinin antigens from four influenza strainsQuadrivalent influenza vaccine antigensInfluenza A and B hemagglutininHA1/HA2 complexSeasonal influenza vaccine antigens

Vaccines containing these antigens induce the production of neutralizing antibodies that bind to the hemagglutinin protein, thereby blocking the virus's ability to attach to host cell sialic acid receptors or preventing the conformational change necessary for viral-host membrane fusion (CDC, 2023; PubMed, 2017).