The time is now: a call to contain H9N2 avian influenza viruses

Abstract

In the past century, we have seen four pandemics caused by human influenza A: H1N1 Spanish influenza (1918–1920), H2N2 Asian influenza (1957–58), H3N2 Hong Kong influenza (1968–69), and H1N1 swine influenza (2009–10).1 Phylogenetic analyses have shown that reassortment of genetic segments from human, animal, or avian influenza viruses is linked to the origin of the four influenza pandemic strains.