In influenza: H* stands for the fifth of several known types of the protein hemagglutinin . N* stands for the first of several known types of the protein neuraminidase . H1N1, which caused the 1918 flu pandemic ("Spanish flu") and currently is causing seasonal human flu and the 2009 flu pandemic ("swine flu") H2N2, which caused "Asian flu" H3N2, which caused "Hong Kong flu" and currently causes seasonal human flu H5N1, ("bird flu"), which is noted for having a strain (Asian-linage HPAI H5N1) that kills over half the humans it infects, infecting and killing species that were never known to suffer from influenza viruses before (e.g. cats), being unable to be stopped by culling all involved poultry - some think due to being endemic in wild birds, and causing billions of dollars to be spent in flu pandemic preparation and preventiveness H7N7, which has unusual zoonotic potential and killed one person H1N2, which is currently endemic in hu...