H1N1

In virology, influenza A virus subtype H1N1 (A/H1N1) is a subtype of influenza A virus. Major outbreaks of H1N1 strains in humans include the 1918 Spanish flu pandemic, the 1977 Russian flu pandemic and the 2009 swine flu pandemic... Some strains of H1N1 are endemic in humans and cause a small fraction of all influenza-like illness and a small fraction of all seasonal influenza, for instance in 2004–2005.[2] Other strains of H1N1 are endemic in pigs (swine influenza) and in birds (avian influenza). https://en.wikipedia.org/wiki/Influenza_A_virus_subtype_H1N1