Influenza B virus (Yamagata lineage) hemagglutinin (HA)

Influenza B virus (Yamagata lineage) hemagglutinin is a critical surface glycoprotein that facilitates viral entry into host cells. It operates by recognizing and binding to sialic acid-containing receptors on the respiratory epithelium, followed by a pH-dependent conformational change that triggers the fusion of the viral and host membranes (UniProt, 2024). As the primary surface antigen, it is the main target for neutralizing antibodies, and its inclusion in quadrivalent vaccines has been standard for over a decade to provide broad protection against Influenza B (CDC, 2023). However, epidemiological data indicates that the Yamagata lineage has not been detected in global circulation since March 2020, suggesting a potential extinction event likely accelerated by COVID-19 mitigation measures (WHO, 2024). Consequently, global health authorities, including the FDA and WHO, have recommended transitioning back to trivalent vaccines that exclude this specific hemagglutinin antigen to streamline production and focus on currently circulating strains (FDA, 2024).

Other names

HemagglutininHAB/Yamagata HAInfluenza B hemagglutininSurface glycoprotein HAB/Yamagata hemagglutinin

Vaccine-induced antibodies bind to the hemagglutinin protein, specifically the globular head or the conserved stem region, to neutralize the virus by blocking its ability to attach to host sialic acid receptors or by preventing the conformational change necessary for membrane fusion (PubMed, 2021).