Influenza virus hemagglutinin (quadrivalent) (HA)

Influenza virus hemagglutinin (HA) is a major surface glycoprotein found on influenza A and B viruses, playing a critical role in the viral life cycle by mediating binding to host cell sialic acid receptors and facilitating membrane fusion (Skehel & Wiley, 2000). The quadrivalent formulation specifically includes HA antigens from two influenza A subtypes (typically H1N1 and H3N2) and two influenza B lineages (Victoria and Yamagata) to provide broad protection against circulating seasonal strains (CDC, 2023). As a primary target for the immune system, HA is the central component of seasonal influenza vaccines, which aim to elicit neutralizing antibodies that block viral entry (FDA, 2024). Beyond vaccines, HA is a target for antiviral research, including small molecule inhibitors and broadly neutralizing antibodies that target the conserved stem region to overcome the challenges of rapid viral mutation (Benton et al., 2020). Understanding HA structure and evolution is essential for vaccine strain selection and the development of universal influenza therapies.

Other names

Quadrivalent influenza vaccine antigensHemagglutinin A/H1N1, A/H3N2, B/Victoria, and B/YamagataInfluenza surface glycoproteinHA1/HA2 subunits

Vaccines containing these antigens induce the production of neutralizing antibodies that bind to the HA head or stem, preventing the virus from attaching to sialic acid receptors on host cells or blocking the conformational change required for membrane fusion (CDC, 2023; Skehel & Wiley, 2000). Antiviral agents like Umifenovir interact with HA to inhibit the low-pH-induced membrane fusion process (Benton et al., 2020).