Funding for this research was provided by:
Medical Research Council (MR/M016560/1, MC_UU_00002/3, MC_UU_00002/3, MR/M016560/1, MC_UU_00002/3, MC_UU_00002/3)
Received: 3 April 2019
Accepted: 13 September 2019
First Online: 2 December 2019
Ethics approval and consent to participate
: Not applicable.
: Consent for publication was not required as no individual person data are reported.
: The authors declare that they have no competing interests.