Haemagglutinin

Haemagglutinin designates surface glycoproteins found on influenza viruses that bind sialic acid receptors on host cells, mediating viral attachment and membrane fusion enabling cellular entry. This critical viral protein exists in multiple subtypes (H1-H18), with evolution through antigenic drift and shift driving seasonal influenza variation and pandemic emergence requiring updated vaccines.

The vaccine industry targets haemagglutinin as the primary influenza vaccine antigen, with vaccine effectiveness depending on antibody responses against circulating strain haemagglutinins. Seasonal vaccine formulations include multiple haemagglutinin subtypes matching predicted circulating strains, requiring annual updates. Antibody responses against haemagglutinin head domain block receptor binding neutralising infection, while stem-directed antibodies demonstrate broader reactivity across subtypes offering potential for universal vaccine development. Structural studies reveal haemagglutinin architecture guiding rational vaccine design targeting conserved regions. As influenza remains a major global health threat, haemagglutinin research continues through improved surveillance and innovative vaccine platforms.