Funding for this research was provided by:
Bill and Melinda Gates Foundation (Oxford Policy Management)
Received: 26 July 2018
Accepted: 26 December 2018
First Online: 21 January 2019
Ethics approval and consent to participate
: The study was approved by the Ethical Review Committee of the lead United Kingdom institution.
: Not applicable.
: The authors declare that they have no competing interests.
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