Influenza A can infect and be transmitted between birds and some mammals (e.g. pigs and humans). Influenza B only infects humans and seals. Influenza infection poses a severe threat to public health and the agricultural economy. This virus mutates quickly by both antigenic drift and reassortment requiring the development and reformulation of new vaccines each year. Influenza strains resistant to almost all known drugs have been identified, making drug development a critical pursuit.