The steps in the infectious cycle are:
Haemagglutinin on the viral surface binds to sialic acid coating the cell surface .
This complex triggers the cell to engulf the virus, forming an endosome within the cell
The viral M2 protein acidifies the endosome, breaking down both the virus and endosome membranes, and releasing viral RNA
Viral RNA enters the cell nucleus and initiates viral replication.
New viral particles are packaged within the cell, and transported through the cell membrane
Neuraminidase on the surface of new viruses cleaves molecules of sialic acid , allowing release of virus. Viral replication initiates the process of cell death, which occurs several hours after release of the virus