Funding for this research was provided by:
Bill and Melinda Gates Foundation (OPP1135522)
Received: 23 November 2018
Accepted: 13 February 2019
First Online: 21 February 2019
Ethics approval and consent to participate
: Ethical clearance was obtained by the national agencies responsible for each survey. All analyses relied on publicly available, anonymized databases.
: Not applicable
: The authors declare that they have no competing interests.
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