Update Increase in Human Infections with Novel Asian Lineage Avian Influenza A

This updated report reinforces previous findings of an increase in human infections of Asian lineage A(H7N9) during the fifth season, noting that human infections were reported in more Chinese provinces, regions, and municipalities than in the four previous seasons combined. The authors discuss the emergence of an HPAI mutation, the development of candidate vaccine viruses, and the isolation of two distinct lineages: the Pearl River Delta lineage and the Yangtze River Delta lineage, with the Yangtze River Delta lineage predominating.