the rt number really needs to be calculated experimentally, and that's exceedingly difficult without widespread serological testing. the modelling hasn't been very predictive, because they haven't been able to get very good data.

i know that the public health people keeping push this number as something to base policy on, and if you could find it easily then it certainly would be, but this is in truth a relic of the theoretical part of their academic training; the difficulty in determining it to the accuracy required makes it a metric of questionable relevance, in actual practice.

so, could the rt number be a key indicator? it could be, yeah - but you'd have to find it with a high level of confidence first, because it's a very delicate metric, and that's almost impossible.

https://www.ctvnews.ca/health/coronavirus/could-rt-number-be-a-key-indicator-of-whether-we-need-return-to-lockdown-mode-1.5037351