Influenza is an RNA virus with a roughly spherical lipid envelope, which is colored yellow on our schematic model. The outside of the virus capsule is covered with 3 specific proteins: Hemagglutinin (purple), Neuraminidase (pink) and the M2 channel (blue). These 3 proteins are involved in virus docking, endocytosis and fusion of the viral membrane to the host cell. The specific types and combinations of the hemagglutinin (H) and neuraminidase (N) on the surface of the virus capsule categorize the strain of the virus. For example H1N1 is swine flu; H1N9 is bird flu. The Spanish flu was also an H1N1 virus. The virus genome is composed of 8 segments of RNA that are released into the host cell upon infection.