HA (hemagglutinin)

Hemagglutinin (HA) is a protein found on the surface of the influenza virus. It plays a crucial role in the virus's ability to infect host cells by attaching to specific receptors on the surface of respiratory cells. Once attached, HA helps the virus merge with the cell membrane, allowing the virus's genetic material to enter and begin infection. Because of its essential role in infection, HA is a primary target for immune responses and is a key component of flu vaccines, aiming to prepare the immune system to recognize and block the virus effectively.