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Geographical distribution of six different subtypes of the novel avian influenza A(H7N9) viruses between March 2013 and December 2014 (N = 99). w1, wave 1 (from 31 March 2013 to 30 September 2013); w2, wave 2 (from 01 October 2013 to 30 September 2014); w3, wave 3 (from 01 October 2014 to 30 September 2015)
