Received: 16 December 2019
Accepted: 13 April 2020
First Online: 28 April 2020
Ethics approval and consent to participate
: The NHS Health Research Authority stated that research ethics committee approval was not required. The study used anonymised routine monitoring data collected under GDPR article 6 1 (e) and article 9 2 (h).
: Not applicable.
: The authors declare that they have no competing interests.