A strain of influenza, the most common cause of flu in humans; also the strain responsible for swine flu - "The current H1N1 virus (swine flu) is a mixture of avian flus that passed through pigs to humans."
Influenza A (H1N1) virus is a subtype of influenzavirus A and the most common cause of influenza (flu) 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 (swine influenza) and in birds (avian influenza) Tıp, İlaç