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For the H1N1/09 virus strain responsible for the 2009 flu pandemic, see Pandemic H1N1/09 virus.
For the current pandemic of Influenza A, see 2009 flu pandemic.
For the 1918 pandemic of Influenza A, see 1918 flu pandemic.
Influenza A virus is a subtype of influenzavirus A and the most common cause of influenza in humans. Some strains of H1N1 are endemic in humans and cause a small fraction of all influenza-like illness and a large fraction of all seasonal influenza. H1N1 strains caused roughly half of all human flu infections in 2006. Other strains of H1N1 are endemic in pigs and in birds . In June 2009, World Health Organization declared that flu due to a new strain of swine-origin H1N1 was responsible for the 2009 flu pandemic. This strain is commonly called "swine flu" by the public media.
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