Footnotes

• JZ and JC are joint first authors.

• Twitter @rahul_kalla

• Contributors XL and JS conceptualised the project. JZ wrote the first draft. All authors critically reviewed the manuscript for important intellectual content. XL is the study guarantor. The corresponding author attests that all listed authors meet authorship criteria and that no others meeting the criteria have been omitted.

• 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.

• Competing interests None declared.

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