Hemagglutinin (Influenza B virus Victoria lineage) (HA)

Hemagglutinin (HA) is the major surface glycoprotein of the influenza B virus, specifically belonging to the Victoria lineage, which is one of the two distinct lineages (alongside Yamagata) that circulate in the human population. It functions as a class I viral fusion protein, responsible for recognizing and binding to terminal sialic acids on host cell surface glycoproteins and glycolipids, followed by mediating the fusion of the viral envelope with the endosomal membrane at low pH (UniProt P03460). In clinical practice, the HA of the Victoria lineage is a vital component of seasonal quadrivalent influenza vaccines, designed to elicit protective neutralizing antibodies (PubMed: 30135358). The protein is composed of two subunits, HA1 and HA2; HA1 contains the highly variable globular head with the receptor-binding site, while HA2 contains the more conserved stalk region. Due to the high rate of antigenic drift in the Victoria lineage, the specific vaccine strain is reviewed and updated annually by the World Health Organization to ensure an optimal match with circulating viruses (WHO, 2024). Challenges in targeting this molecule include the emergence of escape mutants and the potential for egg-based manufacturing to introduce mutations that alter the protein's antigenicity.

Other names

Influenza B Victoria HemagglutininHA proteinSurface glycoproteinB/Victoria lineage antigenHemagglutinin-neuraminidase (in some contexts)Type B influenza hemagglutinin

The hemagglutinin protein acts as the primary antigen in influenza vaccines; it induces the production of neutralizing antibodies that bind to the HA1 globular head domain, thereby blocking the virus's ability to attach to host cell sialic acid receptors and preventing viral entry into the respiratory epithelium (CDC, 2023; PubMed: 30135358).