Recent research has revealed that influenza circulation patterns differ across geographic regions in Peru in inter-pandemic periods [13, 19, 56] . Specifically, in the coastal region surrounding Lima, influenza circulates year round with particularly elevated numbers of cases in the winter time. In contrast, influenza transmission is focused in the cold season in the mountain region and is weakly seasonal in the jungle region where most transmission is limited to the rainy season during the first six months of the year [13, 19, 56] . The timing of the 2009 A/H1N1 influenza pandemic and contemporaneous winter influenza epidemics in Lima is in contrast with the timing of the 1918-1920 influenza pandemic in this city, which occurred during the summer periods of 1918-1919 and 1919-1920 [57] .