Quite simply, if the pre-lockdown R0 figure (number of other people one infected person infects) is, for example, 2.6, then for the infections to drop away as quickly as they came, the R0 figure needs to become the inverse; 1 divided by 2.6, which is 0.38.
Chris Whitty, I think, said that they believe the R0 figure is now somewhere between 0.5 and 1. Even if it were 0.5, it will take longer for the number of new infections and deaths to subside than they built up. If the R0 figure is now 0.8, then it will take nearly 4 times longer for the disease to die out.
Of course the R0 figure is dynamic and can change, is affected by immunity within the population if that is changing, and would also be affected by any relaxation or tightening of the lockdown.
Originally Posted by: Darren S