H3N1 is a subtype of the species Influenza A virus, mostly affecting pigs. The known subtypes of Influenza A virus that create influenza in pigs and are endemic in pigs are H1N1, H1N2, H3N1 and H3N2.
H3N2 viruses can infect birds and mammals. In birds, humans, and pigs, the virus has mutated into many strains. In years in which H3N2 is the predominant strain, there are more hospitalizations.
H3N8 is a subtype of the species Influenza A virus that is endemic in birds, horses and dogs.