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New strain and the R number

There has been news over the last few days about the new strain detected in the South England, with 17 new cases reported in Scotland by today (19th December). Some estimates suggest an increase in the reproductive number of about 0.4.

I run my simple SIR model to fit the UK-wide data and in my model the increase seems to be more than 0.4 – but then R is so much model dependent that it is difficult to compare. Still, it shows how rapid the current increase is, despite all the lockdown measures:

In turn, this is what the results of some simple SIR models look like for Scotland with data up to 30th November (I do not have more recent data at hand) and with the 0.4 increase in the rate starting this week:

This shows how potentially damaging the new outbreak is for the attempt to bring down the disease numbers before the increased mobility (see the green line in the plot above) prior to and during Christmas will result in another outbreak. The graph above is assuming that – apart from the 0.4 increase due to the new strain – there is no effect of this mobility, so the situation is even more risky.

But assuming the increase of the same magnitude as seen in the whole UK data, makes it even more serious:

Well, the message is – this is indeed quite serious and this time I do not think the UK and Scottish government are too soft and too late.