Influenza B Victoria lineage hemagglutinin protein (HA (for Hemagglutinin))

The **Influenza B Victoria lineage hemagglutinin protein** is a trimeric glycoprotein found on the surface of influenza B viruses belonging to the Victoria lineage. It plays a central role in viral infectivity by mediating two critical steps during infection: first, it binds sialic acid-containing receptors on respiratory epithelial cells via its globular head domain; second, after endocytosis into host cells, it undergoes an acid-triggered conformational change that enables fusion between the viral envelope and endosomal membrane—allowing release of viral RNA into the cytoplasm for replication. The structure consists of three identical subunits forming an elongated cylinder with distinct head and stem regions. The head region is highly variable due to immune pressure from neutralizing antibodies; this variability underlies antigenic drift that complicates vaccine design. The stem region is more conserved. Hemagglutinin is both a major antigen recognized by protective immunity following infection or vaccination and a primary therapeutic target for monoclonal antibody therapies under development. Mutations—including deletions—in its sequence can alter antigenicity and impact epidemic dynamics within human populations. Monitoring changes in this protein informs public health responses such as annual flu vaccine composition updates

Other names

Influenza B hemagglutininHemagglutinin (HA)Influenza B/Victoria/2/87-like hemagglutininHA protein of influenza B Victoria lineage

Neutralizing antibodies bind to the globular head or stem region of HA, blocking receptor binding or membrane fusion and thereby preventing viral entry into host cells