Funding for this research was provided by:
Bill and Melinda Gates Foundation (OPP1148933)
South African Medical Research Council (N/A)
United Kingdom Chevening Scholarship (N/A)
South African Research Chair's Initiative of the Department of Science and Technology and National Research Foundation of South Africa (82769)
Text and Data Mining valid from 2019-11-27
Received: 18 July 2019
Accepted: 13 November 2019
First Online: 27 November 2019
Ethics approval and consent to participate
: The Research Governance and Integrity Office of the London School of Hygiene and Tropical Medicine assessed the study protocol and determined that an ethics approval was not required for a systematic review.
: Not applicable.
: The authors declare that they have no competing interests.