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. 2010 Mar 4;5(3):e9533. doi: 10.1371/journal.pone.0009533

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This is an open-access article distributed under the terms of the Creative Commons Public Domain declaration which stipulates that, once placed in the public domain, this work may be freely reproduced, distributed, transmitted, modified, built upon, or otherwise used by anyone for any lawful purpose.

This is an open-access article distributed under the terms of the Creative Commons Public Domain declaration, which stipulates that, once placed in the public domain, this work may be freely reproduced, distributed, transmitted, modified, built upon, or otherwise used by anyone for any lawful purpose.

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Observations are divided into 2 periods: the 2008–09 seasonal influenza period (Sept. 28, 2008 to April 25, 2009 corresponding to CDC 2008–2009 flu season weeks 40–16) and the early pandemic H1N1 2009 period (April 26, 2009 to July 31, 2009 corresponding to CDC 2008–2009 flu season weeks 17–30) since April 26^th was the date of the first confirmed pandemic H1N1 2009 case within the VA system.