Influenza virus hemagglutinin (quadrivalent seasonal strains) (HA)

Influenza virus hemagglutinin (HA) is the primary surface glycoprotein of the influenza virus and a critical target for both prophylactic vaccines and therapeutic interventions. It exists as a homotrimer on the viral envelope and mediates two essential steps of the viral life cycle: binding to host cell sialic acid receptors to initiate attachment and facilitating membrane fusion within the endosome to release the viral genome. Seasonal quadrivalent vaccines are designed to elicit neutralizing antibodies against the HA of four specific strains: two influenza A subtypes (H1N1 and H3N2) and two influenza B lineages (Victoria and Yamagata). While traditional vaccines primarily target the highly variable globular head of HA, research is increasingly focused on the more conserved stem region to develop universal influenza vaccines. Therapeutic agents like Umifenovir (Arbidol) and various monoclonal antibodies also target HA to block viral entry and prevent infection.

Other names

HemagglutininHAInfluenza A virus hemagglutininInfluenza B virus hemagglutininH1 hemagglutininH3 hemagglutininB/Victoria lineage hemagglutininB/Yamagata lineage hemagglutinin

Vaccines induce neutralizing antibodies that bind to the HA head or stem, blocking viral attachment to sialic acid receptors or preventing membrane fusion. Small molecule inhibitors like Umifenovir bind to the HA stem to stabilize the prefusion conformation and prevent the pH-induced conformational change required for fusion.