South West R rate is now above 1 – the highest in the country

The South West’s COVID-19 coronavirus ‘R rate’ is likely to have risen above 1 – and is now the highest in the country – according to the latest modelling by the MRC Biostatistics Unit at Cambridge University.

(But read the caveats – Owl)

And the scientists say it is “very likely” that most regions in England are close to the point at which the virus begins to spread exponentially.

The Cambridge model is only one model that feeds into SAGE’s official regional R rate estimate and is released weekly.

However, it should be noted that Government advisers say regional Rs – which estimate the number of people an infected person spreads the virus to – should be viewed with great caution, because they become mathematically uncertain as the number of cases fall.

And the number of cases in Devon and Cornwall remains very low compared other areas in the country – and the South West is still one of the English regions least affected by the virus. Yesterday, there were only 22 people in hospital in the whole of the South West with coronavirus, with none on a ventilator – and only one hospital death anywhere in the South West in the last two weeks.

Nonetheless, the R rate in the South West is now estimated to be 1.04, but could be anywhere between 0.77 and 1.38 – and is higher than anywhere else in the country.

Viruses can begin to spread exponentially if the R rate rises above 1.

REGION Median R rate Lower R rate Higher R rate
South West 1.04 0.77 1.38
South East 1.02 0.81 1.25
North West 0.92 0.69 1.15
North East and Yorkshire 0.9 0.66 1.12
Midlands 0.78 0.58 1
London 0.92 0.66 1.17
East of England 0.88 0.67 1.12

It comes as the number of confirmed new cases of COVID-19 coronavirus in Cornwall tripled in a week to 19, which saw the the rolling seven-day rate of new cases per 100,000 people rise from 0.9 to 3.3.

However, Devon’s – public health director has said rises in rolling new case rate in some of its Local Authority areas are NOT believed to be linked to visitors to the area.

The county saw five new cases confirmed in Torbay and 12 new cases across the rest of Devon, with three in East Devon, five in Exeter, two in Mid Devon, two in North Devon, and one in the South Hams, with no cases in Teignbridge, Torridge or West Devon.

Plymouth also saw a small rise in the new COVID-19 coronavirus case rate. The latest data from Public Health England shows that the rolling seven-day rate of new cases per 100,000 people has risen from 1.5 to 1.9, with five new cases confirmed.

The figures, for the seven days to July 26, are based on tests carried out in laboratories (pillar one of the Government’s testing programme) and in the wider community (pillar two).

Local Authority New cases per 100,000 people in week until July 26 New cases per 100,000 people in week until July 19 Total number of new cases
Cornwall and Isles of Scilly 3.3 0.9 19
North Devon Torbay 2.1 0 2
Torbay 3.7 1.5 5
Mid Devon 2.4 1.2 2
Exeter 3.8 2.3 5
Plymouth 1.9 1.5 5
Torridge 0 0 0
West Devon 0 0 0
South Hams 0 2.3 1
East Devon 2.1 4.2 3
Teignbridge 0.0 0 4.5 0

By comparison, in Blackburn with Darwen, the rate has risen from 81.2 cases per 100,000 people in the seven days to July 19 to 87.3 in the seven days to July 26 – and a total of 130 new cases have been recorded.

But Prime Minister Boris Johnson has warned that “clearly we now face, I’m afraid, the threat of a second wave in other parts of Europe and we just have to be vigilant”.

Health Secretary Matt Hancock also said the figures showed a “second wave starting to roll across Europe”.

So why does R become less useful?

  • When there are few cases, R is impossible to estimate with accuracy and will have wide confidence intervals that are likely to include one. But this does not necessarily mean the epidemic is increasing.
  • As incidence decreases, R will tend towards 1, and has to be evaluated in conjunction with incidence.

R is an average measure. When incidence is low, an outbreak in one place could result in estimates of R for the entire region to become higher than one.

Conversely, small, local outbreaks will not be detected. Estimates of R based on small numbers may also not capture change in the area fast enough to inform policy in a useful way.

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