Need advice on what is the the most common influenza virus?

Influenza 'A': Influenza 'a' is the most common type of seasonal virus impacting people in the U.S. There are many strains of flu. New influenza viruses are constantly evolving. Mutations can cause small changes in the hemagglutinin and neuraminidase antigens on the surface of the virus. This is called antigenic drift. The proteins are the 'h' and 'n' constituents labeled in 'h5n1' as an example of bird flu.