Quotes About Hemagglutinin

Pandemics generally develop only when a radical change in the hemagglutinin, or the neuraminidase, or both, occurs. When an entirely new gene coding for one or both replaces the old one, the shape of the new antigen bears little resemblance to the old one. This is called "antigen shift.

But sometimes mutations change the shape of the hemagglutinin or neuraminidase enough that the immune system can't read them.