November 27, 2020

expert reaction to latest R number and growth rates for the UK

The government have released the latest estimates for the COVID-19 growth rate and R value.

Prof Mark Woolhouse, Professor of Infectious Disease Epidemiology, University of Edinburgh, said:

“It is encouraging news that the R numbers across the UK are now below one, and may decrease further as the full impact of lockdown becomes apparent. 

“It is worth noting that the falls in R began in the second half of September which may indicate that measures taken during that month did have some impact in some regions of the UK.

“It is very difficult to tease out the impact of several different measures introduced in quick succession. However, these data do raise the question of whether the earlier implementation of measures short of full lockdown would have been sufficient to keep the epidemic in check and prevent local NHS Trusts from being overwhelmed.”

Prof Kevin McConway, Emeritus Professor of Applied Statistics, The Open University, said:

“It’s fairly good news that this week’s range for the UK R number has fallen. It is 0.9-1.0, so there’s a good chance it is below 1. If R is below 1, then the number of infections is expected to fall. That’s in line with other data that we’ve seen this week, from the ONS Infection Survey, from Test and Trace, and from the daily figures for new confirmed cases. The new UK range for the daily growth rate of infections from SAGE and the Government Office for Science has also fallen – it’s now -2% to 0%. 0% means no change, and -2% means that each day will (on average) have 2% fewer new infections than the day before. If infections continued to fall at 2% a day, the number of new infections would halve in about five weeks. If the rate of decrease is in the middle of the SAGE range, 1% decline each day, the number would halve in about ten weeks.

“I’m certainly not saying that this is bad news, but it does need a bit of caution (which is why I say only that the news is fairly good). First, though these figures indicate that the pandemic is decreasing, on average across the whole of the UK, it’s not decreasing very fast. Second, the national figure doesn’t rule out the possibility that R is slightly above 1. SAGE state that R (and the growth rate) are ‘likely’ to be in the ranges they give, but likely doesn’t mean certain. But most importantly, SAGE clearly make the point that the UK figures are averages over places that have different infection conditions, so that the average UK figures for R and the growth rate aren’t necessarily a good guide to what’s happening where you live. For England as a whole, the range for R is the same as the UK range, 0.9-1.0, but the range for the growth rate goes from -2% to +1%, so there’s more of a possibility that infections might still be increasing. The ranges published by the devolved administrations in Scotland and in Wales indicate that infections are probably decreasing there, though the Northern Ireland government is giving a range of 0.9 to 1.1 for R, which could mean that infections remain roughly level there.

“But for the English regions, there are quite large potential differences in the path of the pandemic, according to the ranges for R and growth rates. The only region where the range for R is entirely below 1 is the North West, where it is 0.7-0.9, with a range for the growth rate of -5% to -2%, indicating that the number of infections is very likely falling. In the North East and Yorkshire, the range for R is 0.8-1.0, growth rate -3% to 0%, so also probably falling numbers of new infections. These two regions cover the North of England where infection levels have been highest. (The regional R and growth rate ranges in this SAGE/GOS publication are for NHS regions, unlike many other sets of data that separate the North East of England from Yorkshire.) That’s good news for those hard-hit parts of the country, though both of those regions are large and extensive and the overall regional figures will hide differences between different parts of them. But all the other English regions have a range for R that goes above 1, and growth rate ranges that include the possibility that infection numbers are growing – and for two regions (London and the South East) the ranges do not include any values of R below 1 (the lower ends of their ranges are exactly 1.0) and do not include any negative growth rates (the lower ends are 0, and the upper ends positive, indicating a growing number of infections). Overall, while the position is improving on average, conditions remain risky and the averages do not tell the whole story.

“As always, though, the R and growth rate ranges cannot be totally up to date. They represent a kind of average of the position over the past three or so weeks. That’s because some of the data, on which they are based, is for quantities like hospital admissions or, sadly, deaths, which happen (if they do happen) some time after the people involved were first infected. So today’s ranges cannot yet entirely reflect the lockdown in England, which started three weeks ago, and the way things might have changed since then will not be the same in every region or every UK country. I very much hope next week’s ranges are lower, but we’ll have to wait and see.”

Prof Liam Smeeth, Professor of Clinical Epidemiology, and Dean of the Faculty of Epidemiology and Population Health, London School of Hygiene and Tropical Medicine, said:

“It is increasingly clear that the stricter measures implemented in recent weeks are having an impact. Infections were rising rapidly – and everything we know, including direct experience from the first wave – tells us that infections would have carried on rising and would still be rising now. The collective actions of society have quite literally re-shaped the pandemic. Working together we have been able to control this virus. Obviously the terrible economic and social impacts, and the ongoing health impacts, mean there is little impetus to celebrate. But this should not detract from just what an amazing achievement controlling viral spread has been.

“A road-map towards a much better time for the UK is becoming clear. A period of tiered measures in December is warranted now in order to help allow some social mixing at Christmas that is so important to many. I suspect a further circuit breaker in January or possibly February may well be needed because Christmas will place such upward pressure on transmission rates.

“However, if all goes well, within a few months we are very likely to have vaccinated the older population, care home residents and people with serious underlying illnesses that place then at high risk from Covid-19. Even if the virus continues to circulate at the high levels we were seeing in March or October 2020, hospitalisations and death rates from Covid-19 will be nowhere near the previous levels. The very real fear of the NHS being overwhelmed by severe Covid-19 will recede. This will reduce the massive disruption to NHS services. It will also shape how we tackle the pandemic as a society. Some measures to control spread will still be needed, and some activities restricted. However, once the high-risk groups are vaccinated, this could be the end of severe lockdown measures, school closures and some of the other damaging measures we have been forced to take.  ”

https://www.gov.uk/guidance/the-r-number-in-the-uk

All our previous output on this subject can be seen at this weblink:

www.sciencemediacentre.org/tag/covid-19

Declared interests

Prof Mark Woolhouse: “No COIs to declare.”

Prof Kevin McConway: “I am a Trustee of the SMC and a member of the Advisory Committee, but my quote above is in my capacity as a professional statistician.”

None others received.