Influenza B Yamagata lineage hemagglutinin (HA (commonly used for hemagglutinin, but "Influenza B HA" or "B/Yamagata HA" is more specific))

Influenza B Yamagata lineage hemagglutinin is the lineage-specific surface glycoprotein of the influenza B virus (B/Yamagata lineage), classified as a Class I viral fusion protein and the primary target for neutralizing antibodies and vaccines. HA enables viral entry by binding to sialic acid-containing receptors on host cells, facilitating membrane fusion after endocytosis. The HA gene defines the Yamagata lineage, which is antigenically and genetically distinct from the B/Victoria lineage. The protein's antigenic sites are focal points for immune recognition and drift, which has been slower and less frequent in the Yamagata lineage than the Victoria lineage. HA was historically included in seasonal influenza vaccines but has been excluded since 2023 due to apparent lack of Yamagata virus circulation following COVID-19-related public health measures.

Other names

B/Yamagata hemagglutininInfluenza B hemagglutinin (Yamagata lineage)B/Yamagata HA

Antibodies (from vaccines or natural infection) bind HA, neutralizing the virus by blocking attachment to sialic acid receptors or inhibiting conformational changes required for membrane fusion. Vaccine-induced immunity stimulates production of such neutralizing antibodies.