this is quite interesting - but doesnt answer the question
https://www.technologyreview.com/2020/06/19/1004190/uk-covid-contact-tracing-app-fiasco/
see above - it depends
contact tracing is only one generation - a contact of a contact is NOT traced
the office is NOT gonna be twelve - bit uvva squeeze to get them all within two metres. very cosy. - but they would qualify - prolonged contact in time. But it is not everyone in the building ....not the tea lady
and yes I agree it wd be wasy to get to 60m contacts if you case the net too wide. we actually know how infections spread on transport - from the TB case on an aircraft - only those beside her, fore and aft ( donut) were infected.
https://www.nejm.org/doi/full/10.1056/NEJM199604113341501