Influenza viruses (IFV) are segmented RNA viruses that cause seasonal influenza epidemics and influenza pandemics. IFV A infects birds and some mammals (e.g. pigs and humans), while IFV B only infects humans and seals. Both influenza A and B pose a severe threat to public health and the agricultural economy. Influenza viruses mutate quickly by antigenic drift and reassortment, requiring the development and reformulation of new vaccines each year. Viruses resistant to almost all known drugs have been identified, making influenza drug development a high priority. Concerns about IFV have been further heightened due to the potential for transmission of highly pathogenic avian influenza (HPAI) strains to humans.