Funding for this research was provided by:
Medical Research Council (MR/J014362/1)
World Health Organization (2013/363982-0)
Bill and Melinda Gates Foundation (OPP1099374)
Received: 18 October 2017
Accepted: 26 March 2018
First Online: 13 April 2018
Ethics approval and consent to participate
: Institutional ethics approval was not sought because this is a retrospective study and the databases are anonymised and free of personally identifiable information. The polio surveillance data is reported to WHO under the obligations of the International Health Regulations, and this retrospective research was carried out under this legal framework. The databases used for analysis are anonymised and free of personally identified information, so consent for publication was not sought.
: The manuscript has been approved by the World Health Organisation.
: The authors declare that they have no competing interests.
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