Footnotes

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• Contributors Both authors conceived the idea. MD wrote the initial draft. MD and HA revised subsequent drafts. MD submitted the article. MD and HA revised the article. Both authors are responsible for the content as guarantors.

• Funding The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors. Infrastructure support to HA for this research was provided by the NIHR Imperial Biomedical Research Centre (BRC).

• Competing interests None declared.

• Patient consent for publication Not required.

• Provenance and peer review Not commissioned; externally peer reviewed.