Influenza A virus subtype H3N2, also known as H3N2, is a subtype of viruses that cause influenza (flu). H3N2 Viruses can infect birds and mammals. In birds, humans, and pigs, the virus has mutated into many strains. Hemagglutinin(HA) binds to sialic acid-containing receptors on the cell surface, bringing about the attachment of the virus particle to the cell.