Hemagglutinin (Influenza B virus Yamagata lineage) (HA)

Hemagglutinin (HA) is the primary surface glycoprotein of the influenza B virus, specifically the Yamagata lineage, which diverged from the Victoria lineage in the 1980s [NIH]. It functions as a homotrimeric class I fusion protein, mediating viral entry by binding to sialic acid receptors on host respiratory cells and facilitating the fusion of the viral envelope with the endosomal membrane under acidic conditions [UniProt, Wikipedia]. HA is the principal target for neutralizing antibodies induced by seasonal influenza vaccines and is a major focus for the development of broadly neutralizing monoclonal antibodies and small-molecule fusion inhibitors [NIH]. While the Yamagata lineage has not been confirmed in global circulation since March 2020, HA remains a critical component of historical and some current quadrivalent vaccines [NIH, Eurosurveillance]. Therapeutic strategies targeting HA aim to block the initial stages of infection, either by preventing attachment or by inhibiting the conformational changes required for membrane fusion [NIH]. The protein's high rate of mutation, though slower than that of influenza A, necessitates constant surveillance and periodic vaccine updates to maintain efficacy [Britannica, NIH]. Recent concerns regarding the potential extinction of the Yamagata lineage have led to discussions about removing it from future vaccine formulations to prevent accidental re-introduction from laboratory or vaccine sources [NIH, Eurosurveillance].

Other names

HAHA0HA1HA2HaemagglutininHemagglutinin glycoproteinInfluenza B Yamagata HA

Inhibition of viral entry by blocking receptor binding or preventing membrane fusion