Original: The serotypes that have been confirmed in humans, ordered by the number of known human pandemic deaths, are: H1N1 caused "Spanish Flu" in 1918, "Swine flu" in 2009 H2N2 caused "Asian Flu".
Simplified: The serotypes that have been confirmed in humans, ordered by the number of known human pandemic deaths, are: H1N1 caused "Spanish Flu".