Coronavirus R number and growth rate in south west

There is now a much higher likelihood that the number of new cases if coronavirus in the south west will fall at a faster rate.

This is the latest update by the government today, with SAGE (the Scientific Advisory Group for Emergencies) now estimating that the current rate of reproduction – known as the R number – in the south west now sits between 0.8 and 1.1, while the growth rate is estimated at between -4 per cent and +1 per cent.

This shows a marked shrinkage on last week, particularly in the growth figures, when the R number was between 0.9 and 1.1, while the growth rate was between -2 per cent and +2 per cent.

It means that while SAGE believes the number of new infections could be rising by up to 1 per cent each day, they could also be shrinking by up to four per cent each day, which would be a much faster rate than seven days ago.

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.

All areas of England show a greater possibility for infection shrinkage this week. See the table below for this week’s specific regional figures.

Read next: Coronavirus in Cornwall round up – Friday, September 4

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 -2 per cent and +1 per cent today, compared to -1 per cent to +2 per cent last week.

The rate of infection is also thought to be decreasing slightly 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 it was 0.9 to 1.1.

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 0.9 to 1.0.

SAGE goes on to add however: “These estimates represent the transmission of Covid-19 from several weeks ago due to a time delay between someone being infected and needing healthcare. SAGE does not have confidence that R is currently below 1 in England.”

Region R Growth rate % per day

England 0.9-1.0 -2 to +1

East of England* 0.8-1.0 -5 to 0

London* 0.9-1.1 -3 to +2

Midlands* 0.8-1.0 -6 to 0

North East and Yorkshire* 0.8-1.0 -3 to 0

North West 0.8-1.0 -3 to 0

South East* 0.8-1.0 -4 to +1

South West* 0.8-1.1 -4 to +1

*Particular care should be taken when interpreting these estimates as they are based on low numbers of deaths and/or clustered outbreaks within this area and are insufficiently robust to inform policy decisions alone.