The WHO global influenza surveillance and response system (GISRS)—A future perspective

Hay, Alan J; McCauley, John W

There is a clear lack of fundamental knowledge to predict the likelihood that a particular subtype could cause a pandemic. That it was another different H1N1 virus that caused the latest pandemic, 57 and not a novel subtype different from that already circulating, emphasises the adventitious nature of the emergence of a pandemic virus. That a number of different H1N1 subtype viruses have transferred to pigs points to a predilection of the H1N1 avian viruses for mammalian transmissibility. Moreover, the recent sporadic human infections by swine "variant," H1N1v and H3N2v, viruses, 58 once again begs the question as to the extent to which pandemic viruses recycle. 59 Nevertheless, the persistent circulation of the H3N2 subtype for almost 50 years attests to its resilience and ability to continue to adapt in the human population.