Text and Data Mining valid from 2018-05-31
Received: 21 December 2017
Accepted: 9 May 2018
First Online: 31 May 2018
: The first and last authors share interest in Infectious Disease Epidemiology and belong to the Hokkaido University Graduate School of Medicine.
: The present study analysed only published and openly available data. As such, the present study did not require ethics approval.
: The authors declare that they have no competing interests.
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