Seasonal Migration between North-China and South-China. (A) Provinces in China were partitioned based on broad incidence seasonality patterns, inferred using the bi-monthly distribution of sequence samples (Additional file 1: Figure S2). The partitioning of the provinces divided China into a northern (NC) and a southern (SC) seasonality clusters. SC maintains two seasonal peaks while NC displays a single season during winter months. (B) The location of cities in the provinces included in the analysis colored by their seasonal partitioning. (C) In yellow (purple), the inferred distribution of time for which sampled SC (NC) sequences have remained in SC (NC) following a migration event. (D) The inferred mean (90% CI) number of migration events between NC, SC and the other (OT) global communities.