Funding for this research was provided by:
Medical Research Council
Received: 7 September 2020
Accepted: 9 November 2020
First Online: 2 December 2020
Ethics approval and consent to participate
: The Research Governance and Integrity Office of the London School of Hygiene and Tropical Medicine approved this analysis (reference 17018), and declared it not to require separate review by the Ethics Committee as it involved secondary analyses of data already in the public domain.
: Not applicable.
: The authors declare no competing interests.