Funding for this research was provided by:
Bill & Melinda Gates Foundation (OPP1199234)
Wellcome Trust (101815/Z/13/Z)
Received: 29 November 2019
Accepted: 22 May 2020
First Online: 1 June 2020
Ethics approval and consent to participate
: Ethical approval was obtained from institutional review boards of each country by the institution that administered the surveys. The Johns Hopkins Bloomberg School of Public Health also issued ethical clearance. All analyses relied on anonymized databases.
: Not applicable.
: The authors declare that they have no competing interests.