Funding for this research was provided by:
Commonwealth Scholarship Commission (NGCA-2015-051)
Medical Research Council (MR/R015600/1)
Bill and Melinda Gates Foundation (OPP 1033751)
Received: 18 April 2019
Accepted: 22 August 2019
First Online: 16 September 2019
Ethics approval and consent to participate
: The process of obtaining ethical approvals, informed consent, and arranging logistical procedures for field surveys were handled in-country by the Nigeria Ministry of Health, with technical support by the WHO.
: Not applicable.
: The authors declare that they have no competing interests.