This picture provides a 3D graphical representation of a generic influenza virion?s ultrastructure, and is not specific to a seasonal, avian or 2009 H1N1 virus. In this particular view, a portion of the virion?s protein coat, or ?capsid?, has been cut away, revealing its inner nucleic acid core proteins. Note the key to the right identifying the virion?s protein constituents. There are three types of influenza viruses: A, B and C. Human influenza A and B viruses cause seasonal epidemics of disea