The first pandemic wave in Peru affected mostly school age children in the Lima metropolitan area. This pattern was not the result of testing or age population composition differences since testing rates were consistent across age groups in this region ( Figure C in Text S1), and the population age distribution is very similar across geographic regions of Peru. The second major peak of cases affected all age groups and regions of Peru. Other countries experienced multiple pandemic waves including Mexico, the United States, and the United Kingdom, and Japan [45] [48, 49, 50] whereas a number of countries, particularly in the Southern Hemisphere, have experienced only a single pandemic wave in 2009, including Chile [51] , Argentina [52] , Australia [53, 54] , and New Zealand [53] . Other countries in Europe also experienced a single main wave in fall 2009 [55] .