Janik, I think that PT's graph may be from page 19 of this report. There is more on methodology in the text
https://assets.publishing.service.go..._-_week_36.pdf
https://assets.publishing.service.go..._-_week_36.pdf
[https://twitter.com/danbloom1/status/1438023721017556994?s=21
https://twitter.com/hemantmehta/status/1438113265284956163?s=19
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