Pandemic strains of influenza are noted for, among other things, their tendency to utterly ignore the routine seasonal patterns of flu. See: The 2009 pandemic,

Pandemic strains of influenza are noted for, among other things, their tendency to utterly ignore the routine seasonal patterns of flu. See: The 2009 pandemic, which kicked off in late spring, when the major wave of seasonal influenza is on the way out, if not over entirely.