ON THE R-ISE
Coronavirus R rate up for second week in a row – as UK hits 1
THE coronavirus R rate is up for the second week in a row - with the overall average for the UK reaching 1.
New data has revealed that almost every region of England is now pushing the crucial value, which could suggest the epidemic is growing.
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When the value is below one, it means transmission of the virus is no longer high.
But the reality is the true R rate probably lies somewhere between the upper and lower estimates.
Experts warn that as Covid cases are much lower than they were at the peak of the pandemic, the R rate is more sensitive to even small outbreaks.
The latest figures published today by the Scientific Advisory Group for Emergencies (SAGE) shows that the range across the country is now hitting 1.
It was just under the crucial value at between 0.8-0.9 when the weekly numbers were updated last Friday.
Regional breakdown
The regional breakdown also shows that East Anglia is the only part of the country where the R rate is below 1.
In the North East and Yorkshire as well as the Midlands both saw the same increases, with the range up from 0.7-0.9 last week to 0.8-1 this week.
London is also pushing above 1 now at 0.8-1.1 this week from 0.8-1 last week.
The South West and the South East have stayed at the same range as the previous week, though still teetering close to 1.
But Government advisers say that the latest 'growth rate' shows that the epidemic is somewhere between remaining stable and shrinking by five per cent every day.
This measurement reflects how quickly the number of infections are changing day-by-day.
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What does R rate mean?
R0, or R nought, refers to the average number of people that one infected person can expect to pass the coronavirus on to.
Scientists use it to predict how far and how fast a disease will spread - and the number can also inform policy decisions about how to contain an outbreak.
For example, if a virus has an R0 of three, it means that every sick person will pass the disease on to three other people if no containment measures are introduced.
It's also worth pointing out that the R0 is a measure of how infectious a disease is, but not how deadly
It is an approximation of the change of number of infections each day, according to Government experts.
If the growth rate is greater than zero (positive), then the disease will grow, but less than zero then the disease will shrink.
A Sage spokesperson said: "A growth rate between 0% to -5% means the number of new infections is somewhere between remaining stable and shrinking by 5% every day.
"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."
The rise in the R rate comes despite new figures today showing that Covid cases may be starting to level off.
In England, 3,700 people in England are testing positive for Covid-19 every day, according to the Office for National Statistics.
That's a 12 per cent drop on the previous week (July 20 to 26), when figures showed 4,200 people were infected on a daily basis.
Experts suggest that Sage's R rating estimate may lag behind the ONS figures because the Government scientists using a variety of data sources.
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Prof Steven Riley, an infectious disease expert at Imperial College London, said: “Scientists are using a variety of data sources to track the R value.
"On average, the data used for SAGE R estimates is a little slower than ONS data.
"Therefore, the R rise from SAGE is better compared with previous ONS reports.”
R rate caution
Meanwhile, experts have issued caution over the accuracy of the R rate estimate when cases are so few.
Prof Keith Neal said that local Covid clusters can also push the R rate up for an entire region when it may just be one small area.
The epidemiologist at the University of Nottingham said: “Making estimates of R with small number of cases becomes increasingly difficult and inaccurate. Hence the wide range of the estimates.
“A local cluster in one part of a region such as Leicester in the East Midlands can give a value over 1 overall for the region but the figure would be much lower in the rest of the region.
Making estimates of R with small number of cases becomes increasingly difficult and inaccurate
Prof Keith Neal
“These local clusters need to be identified and managed with locally targeted measures.
“For many parts of the country infection rates continue to fall but caution and avoidance of high risk mixing needs to continue.
“If R goes above 1 this is likely to be due a mixture of areas with some above and below 1.
“The best way the public can help control Covid-19 is to get tested if they have symptoms, and if positive isolate and identify their contacts.”
Speed of transmission
The R rate gives an indication of whether or not the Covid-19 outbreak is growing.
Above one, and it's a sign the epidemic is spreading, while below one indicates an outbreak in decline.
But critics of the R rate have pointed out it does not tell us how quickly an epidemic is changing.
That's why the Government introduced the new growth rate measure,which gives insight on the size and speed of change, whereas the R rate only gives information on the direction of change.
Neither one measures is deemed better by the Government, but "each provide information that is useful in monitoring the spread of disease".
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One thing to note is as the number of infections fall, the measures do become less useful, the number of new cases of the disease, for example.
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Dr Kyrychko explained: "As the number of confirmed cases becomes smaller, the estimates of the growth rate and the R number become more sensitive in a sense that even a relatively small local outbreak can have a major effect on increasing the R number."
She said while the R rate is important, it is crucial to have a detailed breakdown of cases at a local level, "so community transmission can be quickly identified and contained".
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