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. 2013 Jun 11;8(6):e65342. doi: 10.1371/journal.pone.0065342

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© 2013 Octavia et al

This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are properly credited.

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Four subpopulations (I to IV) as determined by STRUCTURE analysis are indicated with curly brackets. Isolates associated with 6^th, pre-7^th and 7^th pandemics are indicated with an arrow.