Understanding the R value and its expected rise in the South West

The director of Public Health Devon has explained some of the common misconceptions surrounding the 'R' rate, as it is expected to rise in the South West over the coming days.

The 'R' value, also known as the reproduction rate, is a key metric that helps gauge the rate of the spread of coronavirus, helping the government make decisions on how to ease lockdown.

The South West currently has the lowest number of coronavirus cases compared to any other region in England. Devon in particular has the fifth lowest number of recorded cases of all 150 upper tier local authorities.

However, as lockdown restrictions were eased a large number of visitors travelled to the area, sparking some concerns that the South West's 'R' rate will rise over the coming days.

Director of Public Health for Public Health Devon, Dr Virginia Pearson, has released a statement alleviating some of these fears, saying that the figures should be "treated with a little caution".

She commented: "The R value is an important regional barometer based on modelling data, but while it provides an estimate of ongoing transmission, it alone cannot determine the rate of growth of coronavirus and does not accurately reflect Devon's local data on the ground. As such it should be treated with a little caution.

"The South West R value spans from Isles of Scilly to Bristol, and while there have been hotspots in other parts of the region that increase the R value, Devon's figures have remained low.

"We have the fifth lowest number of recorded cases when comparing Devon to all 150 upper tier local authorities and the consistency of the numbers suggest that levels have plateaued recently. That's in part due to our residents adhering to lockdown, and heeding national guidance around staying home and social distancing.

"We have done well in that regard and need to keep that up.

"We continue to work closely with our Public Health and NHS colleagues to ensure the safety of our Devon residents, and we wait to hear the government's response to this latest R rate announcement."

Dr Yvonne Doyle, medical director of Public Health England, added: "Our estimates show that the regional R numbers have increased although they remain below 1 for most of England – this is to be expected as we gradually move out of lockdown.

"It is vital that everyone continues with social distancing, practicing good hand hygiene and must remain at home and order a test if they have symptoms."

Professor Debra Lapthorne, Regional Director PHE SW & Regional Director of Public Health NHS England South West, commented: "The timing of the initial wave of infection was very different in each region, and consequently there will be some regional variation in R even now. Alongside the North West, and East of England, the South West had one of the lowest levels of activity prior to the lock down, due to a delayed spread into these regions.

"It is encouraging to see that the South West continues to see comparatively lower numbers of cases and deaths from COVID-19. We need to ensure all our communities continue to follow government guidance on social distancing and self-isolation. As lock down measures are eased across the country, it is vitally important we do everything we can to slow the spread of the virus and save lives.

"It's important to note that the R value should really be considered alongside incidence, and that a region may have a higher value of R, but a lower number of cases reported than another region with a lower value of R.

"The R value increase across England, and for the South West, is to be expected, given the relaxation from lock down and subsequent increase in contacts within the community. While the figure is helpful at a regional level, we advise treating any modelling data with caution."

The R number is only one component that determines the rate of growth of the epidemic, and does not say anything about the rate of occurrence of new infections, the prevalence of infection across communities and the current burden faced by the healthcare system. It should, therefore, not be used as the sole indicator of the current threat posed by an epidemic.