 [ Symptoms ] what is swine influenza h1n1 [ Disease ] swine influenza h1n1 is a very contagious respiratory disease caused by a strain of the influenza type a virus swine influenza h1n1 or swine flu h1n1 originally occurred only in pigs or rarely in those who were around pigs however a new strain of the swine flu h1n1 virus has been able to spread from person to person outbreaks of the new swine flu h1n1 started to occur between humans in march 2009