Coronavirus R number and growth in south west above national average

The potential growth rate of new coronavirus cases in the south west is now estimated to be above the national average and the highest in the UK – although in real terms of case numbers figures remain low.

In the weekly Friday update on its website this afternoon, the government said that the current rate of reproduction – known as the R number – in the south west was now thought to sit between 0.8 and 1.1, while the growth rate was estimated at between -1 per cent and +2 per cent.

The estimated growth rate reflects how quickly the number of infections changes day by day, as way of keeping track of the virus.

If the growth rate is greater than zero then the epidemic is growing. If the growth rate is less than zero then the epidemic is shrinking.

The size of the growth rate indicates the speed of change.

It means that in the south west as a whole SAGE (the Scientific Advisory Group for Emergencies), which advises the government, believes while the number of new infections could be shrinking by up to 1 per cent each day, it could be growing by up to 2 per cent.

This is despite data on Wednesday showing that the number new cases specifically in Cornwall in the seven days leading up to August 16 was a third lower than it had been three weeks earlier.

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The possible +2 per cent rise is the highest ‘top percentage’ prediction in the UK, meaning SAGE thinks the region has the potential for the fastest growth of infection.

While most other regions of the UK are showing a predicted decline or static growth, the south west is one of only three – along with London and the North West – to be showing a positive increase. See the table below for specific regional figures.

It should be noted that in the government figures the south west includes Cornwall, Devon, Dorset, Somerset, Wiltshire and Gloucestershire, with these weekly updates not breaking them down into counties.

Last week the south west had a growth rate of -5 per cent to +1 per cent, when a much larger decline in infections was estimated.

SAGE also recognises there are limitations in both R number and growth rate, stating: “The growth rate is an average value that can vary. When case numbers are low, uncertainty increases.

“This could happen when only a very small proportion of people are infected, or the geographical area considered has a very small population.”

This is particularly relevant to the south west.

It goes on to add that a higher percentage number “does not necessarily mean the epidemic is increasing in that region, just that the uncertainty means it cannot be ruled out.”

Nationally the UK as whole has a growth rate of between -3 per cent and +1 per cent today.

The rate of infection is also thought to be increasing very slightly in the south west and in the UK as a whole.

In the south west it means that for every one person with the infection a further 0.8 to 1.1 people are likely to go on to be infected. Last week the range was 0.8 to 1.0.

The values are shown as a range, with the most likely true values somewhere towards the middle of the range.

Nationally the UK’s R number is now 0.9 to 1.1, compared to 0.8 to 1.0 last week.

The government website states: “The UK estimates of R and growth rate are averages over very different epidemiological situations and should be regarded as a guide to the general trend rather than a description of the epidemic state.”

Region R Growth rate % per day

England 0.9-1.0 -3 to 0

East of England* 0.8-1.0 -3 to 0

London* 0.9-1.1 -2 to +1

Midlands 0.8-1.0 -4 to 0

North East and Yorkshire* 0.8-1.0 -4 to 0

North West 0.9-1.1 -2 to +1

South East 0.8-1.0 -4 to 0

South West* 0.8-1.1 -1 to +2

*Low case numbers and/ or a high degree of variability in transmission across the region means these estimates are insufficiently robust to inform policy decisions.