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. 2015 Sep 28;5:14171. doi: 10.1038/srep14171

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Copyright © 2015, Macmillan Publishers Limited

This work is licensed under a Creative Commons Attribution 4.0 International License. The images or other third party material in this article are included in the article’s Creative Commons license, unless indicated otherwise in the credit line; if the material is not included under the Creative Commons license, users will need to obtain permission from the license holder to reproduce the material. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/

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(a) Geographic distribution of H1N1 HA sequences provided by the China CDC and obtained from a public database from 1977 to 2008. The map was reconstructed using OpenStreetMap (http://www.openstreetmap.org/) with further modification, and is for illustrative purposes only. (b) Dynamic changes in the percentage of antigenic clusters in South and North China. The underlying bar represents the circulation period of each antigenic cluster in South and North China and the earliest appearance of a new antigenic cluster is marked with a star. (c) Co-circulation of antigenic clusters in South and North China. Co-circulation was measured as the entropy of co-circulating antigenic clusters.