Influenza A hemagglutinin H1 (HA (H1 subtype))

**Influenza A hemagglutinin H1** is a trimeric glycoprotein on the surface of the influenza A virus subtype H1N1, playing a central role in mediating *both* attachment to host cell sialic acid receptors (primarily in the upper respiratory tract) and viral membrane fusion upon acidification in endosomes[1][3][5][9]. It is the principal antigen for neutralizing antibodies, making it the critical immunogenic target for seasonal and pandemic influenza vaccines[9][1][5]. Mutations in H1 hemagglutinin underlie antigenic drift, resulting in the need for annual flu vaccine updates and enabling pandemic emergence when antigenic properties change dramatically[8][6]. There are multiple subtypes of hemagglutinin, but the H1 variant is specifically associated with seasonal influenza and notable pandemics—including the 1918, 1977, and 2009 outbreaks[6][5][1].

Other names

hemagglutininHAH1 hemagglutininH1N1 hemagglutinininfluenza hemagglutinin

- Inhibition of viral entry by neutralizing antibodies binding to HA globular head or stem region, blocking receptor binding or membrane fusion[9][8][1] - Indirect reduction of viral spread when hemagglutinin-mediated infection is prevented by immune response or specific antivirals