Changes Through Shift and Drift

Type B viruses are incapable of "shift". They can only "drift", which type A viruses also can do. "Drift" is a gradual change of the hemagglutinin or neuraminadase proteins on the surface of a particular strain of influenza. The change occurs in response to antibodies in people who have been exposed to it. "Drift" is an ongoing process in both types of virus, and it necessitates ongoing changes in influenza vaccines.⁸⁴

The surface proteins of the influenza virus are responsible for the replication and spread of the virus throughout the entire respiratory system - the nose, sinuses, throat, ear and lungs.⁸⁵

Rod-shaped H protein enable the virus to attach itself to a cell in the respiratory system and penetrate it.⁸⁶ Mushroom-shaped N protein allows the virus to escape from an infected respiratory cell and infect new cells.⁸⁷