Coronavirus R number in UK 'rises to between 0.9 and 1.1'

21 August 2020, 14:19

The R number in the UK has now risen to between 0.9 and 1.1, according to Sage. Picture: PA

By Nick Hardinges

The UK's coronavirus R number has risen to between 0.9 and 1.1, according to the government's scientific advisory group.

According to data released on Friday by the Government Office for Science (GOS) and the Scientific Advisory Group for Emergencies (Sage), the UK's infection rate has now increased from the range of between 0.8 and 1.0 one week ago.

The R number represents the number of people on average someone with Covid-19 will likely go on to infect. If it creeps above 1, that suggests transmission is beginning to get out of control.

Sage also said the rate of growth - which shows how quickly the number of infections is changing day-by-day - in the UK may still be on the rise

The country's latest growth rate is between minus 3 per cent to plus 1 per cent, a slight increase on what was previously between minus 4 per cent to minus 1 per cent last week.

This means the number of new positive cases is somewhere between shrinking by 3 per cent and growing by 1 per cent every day, with the most likely value being somewhere in the middle of that range, according to experts.

What is the R rate?

In England, the R number stands between 0.9 and 1.0, and the growth rate is between minus 3 per cent and zero.

However, the estimates do not reflect the recent changes in transmission because the data used to establish R and the growth rate tell us the situation from a few weeks ago - this means we are effectively seeing the reality of a few weeks ago.

Due to the figures being based on estimates, experts admit there may be a degree of uncertainty with them.

A time delay between initial infection and the need for hospital care usually means it may take between two to three weeks for the changes in the spread of coronavirus to be reflected in the estimates.

But models that use Covid-19 testing data, which have less of a time delay, indicate higher values for R in England, the GOS statement said.

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It added: "For this reason, Sage does not have confidence that R is currently below 1.0 in England.

"We would expect to see this change in transmission reflected in the R and growth rate published over the next few weeks as we gain more certainty of what is currently happening."

The scientists warn that the estimates are less reliable and less useful in determining the state of the epidemic when disease incidence is low, or where there is significant variability in the population, for example during local outbreaks.

When this is the case, estimates of R and growth rate become insufficiently robust to inform policy decisions, they add.

Both are average measures and will smooth over localised outbreaks or over short periods of time.

In the east of England, the growth rate has changed from between minus 5 per cent and minus 1 per cent to between minus 3 per cent and zero.

The R number remains unchanged from last week at 0.8-1.

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In London, the growth rate is between minus 2 per cent and plus 1 per cent, compared to between minus 4 per cent and zero last week. The capital has seen the R-value change from 0.8-1 to 0.9-1.1.

The Midlands has a growth rate of minus 4 per cent to zero, compared with between minus 5 per cent and minus 1 per cent last week. Its R-value is unchanged at 0.8-1.

In the North East and Yorkshire, the growth rate remains unchanged since last week and is somewhere between minus 4 per cent and zero. Its R number is 0.8-1.

The growth rate in the North West is between minus 2 per cent and plus 1 per cent, a slight change from between minus 3 per cent and plus 1 per cent. The R-value here is 0.9-1.1.

In the South East, the growth rate is between minus 4 per cent and zero, compared with between 5 per cent and minus 1 per cent last week. The R-value in the region is 0.8-1.0.

The South West has a growth rate of minus 1 per cent to plus 2 per cent, compared to between minus 5 per cent and plus 1 per cent last week. Its R-value is above one, with a range of 0.8-1.1.

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