Funding for this research was provided by:
Bill and Melinda Gates Foundation (OPP1162384)
Received: 12 February 2020
Accepted: 14 July 2020
First Online: 22 July 2020
Ethics approval and consent to participate
: Ethical approval was not required for this study as it is based on publicly available data. The study didn’t involve individual level data.
: All authors read and approved the final manuscript.
: The funding agents had no role in the design, analysis and write-up of the manuscript. The views expressed in the manuscript reflect only the authors’ view and not that of any organization. The authors declare that they have no competing interests.