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Article History

Received: 26 March 2019

Revised: 12 September 2019

Accepted: 17 September 2019

First Online: 11 October 2019

Competing interests

: The authors declare no competing interests.

: Public Health England operates under Section 251 of the National Health Service Act 2006 and its current regulations, the Health Service (Control of Patient Information) Regulations 2002.

: No funding was required for this study.

: The data are available and can be provided by the Office for Data Release (ODR). The authors are employed by Public Health England operated under Section 251 of the National Health Service Act 2006 to access and analyse the data. Authors employed outside of Public Health England did not have direct access to the data but collaborated on the methodology, results and paper.

: This work is published under the standard license to publish agreement. After 12 months the work will become freely available and the license terms will switch to a Creative Commons Attribution 4.0 International (CC BY 4.0).