| A subtype of INFLUENZA A VIRUS comprised of the surface proteins hemagglutinin 1 and neuraminidase 1. The H1N1 subtype was responsible for the Spanish flu pandemic of 1918 and for swine flu. | infection: coordinate IM with INFLUENZA, HUMAN (IM) in humans, or INFLUENZA IN BIRDS (IM) in birds, or ORTHOMYXOVIRIDAE INFECTIONS (IM) in other animals | Other names H1N1 Virus; Viruses, H1N1; Virus, H1N1; H1N1 Viruses; H1N1 Virus | ||