Both H2N2 (1957 pandemic) and H3N2 are likely to have arisen by exchange of genes between avian and human flu viruses, possibly following dual infection in humans.

• H2N2（1957年大流行）和H3N2都可能源于禽类和人类流感病毒的基因交换，有可能在人类的双重感染后发生。