In the spring of 2009 a novel influenza A virus (H1N1) of swine origin was identified in the USA and Mexico and rapid spread led to the declaration of a global influenza pandemic by the World Health Organization in June 2009. 

The virus, which derives six genes from triple-reassortant North American swine virus lineages and two genes from Eurasian swine virus lineages, predominantly affected children and young adults with a low incidence of acute illness in those over 60 years of age. By June 2010, cases had been identified in over 200 countries and territories worldwide and over 18 000 associated deaths were reported. ...