Funding for this research was provided by:
Bill and Melinda Gates Foundation (OPP1181807)
ExxonMobil Foundation (NA)
Received: 7 June 2018
Accepted: 1 November 2018
First Online: 17 January 2019
Ethics approval and consent to participate
: All data included in this analysis were obtained from studies conducted with ethical approvals from the country of origin. Use of existing data which are fully anonymized and which researchers cannot trace back to identifiable individuals does not require the review of the Ethics Committee under the guidelines of the Oxford Central University Research Ethics Committee.
: Not required
: The authors declare that they have no competing interests.
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