Influenza viruses are members of the family Orthomyxoviridae and are divided into three genres, A, B, and C. Influenza A and B viruses are most relevant clinically, since they cause severe respiratory infections in humans. Influenza A (H1N1), A (H3N2), and one or two influenza B viruses (depending on the vaccine) are included in each year’s influenza vaccine.
Influenza A (H3N2) is a subtype of viruses that causes influenza. H3N2 Viruses can infect birds and mammals. In birds, humans, and pigs, the virus has mutated into many strains. H3N2 is increasingly abundant in seasonal influenza.