Wasn’t there a study somewhere that concluded that the risk with no mitigation (distancing or masks) was around 1 in 11,000?
That was the RSSB study. Possibly the worst study of anything I've seen over the entire COVID outbreak, and I've read some stinkers. Somebody at the RSSB evidently fancied paying someone at a consultancy, who fancied doing a crowd dynamics study. That isn't in any sense what was called for, but presumably that was what the computer program they'd just downloaded did.
They made a whole series of assumptions ranging from the improbable to the absolutely incorrect, and fed them into the model wherever they needed actual data. They then modelled the average period of time you'd be within 2m or 1m of other passengers, based on normal behaviour, and modified for the addition of one-way systems (but not for passengers actively avoiding each other - apparently the one way systems in this analysis are smarter than the passengers).
All of this magically spat out a figure of 1 in 11k, although one of the inputs was the prevailing infection rate in the UK at the time, so we're probably closer to 1 in 2k if they reran it now even based on their meaningless analysis.
The best bit was when somebody asked them about masks at the last minute and they clearly hadn't even though of that, so they grabbed a figure of masks being 44% safer from a sub-table of the WHO-funded masks analysis (that figure has its own problems), and they decided to just multiply by the 1 in 11k to say that it must be 1 in 20k. No consideration that the figures they dumped into the mincer to create the 1 in 11k might already take masks into account, or that the 44% safer figure was really nothing to do with public transport at all, just a multiplication.
Absolute rubbish