As soon as the government released its modelling of the pandemic a few days ago, I realised something was badly wrong. The modelling showed infections increasing even under lockdowns, which obviously wasn’t happening. The crucial parameter here is R, the number of new infections generated by each existing infection. If R is greater than 1, the number of infections grows exponentially, but if R is less than one, it declines, eventually approaching zero. The knife-edge case is R=1, when the number stays constant.
On checking the paper on which the modelling was based, I found that it did indeed assume R>1, even with social distancing. This was less surprising when I realized it was based primarily on data from the initial outbreak in Wuhan, before the lockdown in China had taken full effect. (I later discovered that the report had been given to the government in February, which makes its…
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Utopia, you are standing in it! 
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