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The Office for National Statistics (ONS) and government have published the latest data from their infection survey and estimates for the COVID-19 R number in the UK respectively.
Commenting on the R number:
Dr Yuliya Kyrychko, Reader in Mathematics, University of Sussex, said:
“Latest estimates of the R number combined with growing number of new infections over the last several days suggest that the number of infections was and is continuing to grow across England. This makes the current situation very delicate, especially with opening of schools next week because increased social interactions and contacts associated with schools should be carefully balanced by the reduction of contacts elsewhere if possible to avoid a significant growth in new infections.
“The increase in positive cases in Pillar 2 testing and low death rates suggest that majority of cases are not causing major health crisis at the moment, but this means that only a very robust and efficient track-and-trace program would stop this from reaching more vulnerable groups and becoming a larger and deadlier outbreak.”
Commenting on the R number:
Dr Konstantin Blyuss, Reader in Mathematics, University of Sussex, said:
“The latest data show that the estimates of R number in all regions of England, and the UK as a whole, have either remained the same or grown since last week. In fact, yesterday saw the biggest recorded number of new case in the UK since the middle of June. Particularly worrying is the observation that now the rate of growth of new infections in all regions may be exceeding one. This is one of the major distinction between the UK and the recently observed major growth in new COVID-19 cases in several European countries, where the outbreaks were much more localised in nature. Obviously, the problem with this is that if the new cases continue to grow, it can become very hard to quickly contain the infection if it covers a large part of the country.
“Considering these new data in the context of schools opening next week, it is of paramount importance to bear in mind that infections are still currently widespread in the general population, and the study from PHE last week showed that infections are more easily passed from school children to staff, and between staff, rather than between school children, indicating that particular attention should be paid to making provisions for preventing outbreaks in school, which can be not only very disruptive, but also potentially resulting in some major local growth of infections. A related issue concerns considerations regarding whether the companies should continue work from home or return to office, especially if such transition is taking place in parallel to opening schools, i.e. increasing contacts in population. If people can work from home, this would naturally reduce their potential exposure to infection, while also preventing the possibility of them inadvertently spreading it to other people. In this respect, with schools opening being a priority, perhaps it would be a good idea to first understand the effects of schools opening on the dynamics of the epidemic, and then review working from home/office arrangements in light of how the epidemic behaves.”
Prof Kevin McConway, Emeritus Professor of Applied Statistics, The Open University, said:
“The weekly update on findings from the Office for National Statistics (ONS) Infection survey, as well as the updated estimates of the R number and the growth rate of new coronavirus infections from SAGE and the Government Office for Science, have both been published, and my interpretation is that both of them indicate that the rate of new infections is approximately stable at the national level. It might be increasing very slowly, or it might be falling very slowly. Because it’s impossible to detect every new infection, there is inevitable statistical uncertainty in these estimates – but I think we can be very confident that the rate of infections was not changing fast (up or down) in the weeks covered by the new data. I’m sure everyone would be happier if we could be reasonably confident that the infection rate is falling. It may well be falling, but at least these estimates indicate that it is not rising fast, nationally, and even if there is a slow rise, that doesn’t mean that it will continue to rise. We just can’t be sure.
“Unlike many of the other sources of information on new cases, the ONS infection survey estimates aren’t affected by changes in the numbers of tests done as a result of people having symptoms. Those tested are a reasonably representative sample of the community population of England, and now also Wales and Northern Ireland. The infection survey indicated a slow increase in the number of infections from a low point at the end of June, but ONS have been saying now for several weeks that this increase appears to have levelled off, and the evidence for that levelling off gets stronger weekly. The latest report covers testing up to 20 August. It’s particularly encouraging that the estimated rate of new positive swab tests, indicating new infections, is lower than last week’s estimate, and last week’s was lower than the previous week’s. ONS are cautious about this finding, because there is a considerable amount of statistical uncertainty in the figures. That’s because, despite the fact that this is a large survey with around 20,000 people tested each week, the current number of infections in England (and Wales) is low. Only 6 new infections were found, amongst the people tested for the survey, in the two weeks ending 20 August, so the rate of new infections just can’t be estimated all that precisely. Because of this uncertainty, ONS say that they cannot be confident that the rate of new cases in England is falling, so they continue to report that it remains unchanged. I think that’s reasonable – we can’t be anywhere near certain that new infections fell in the week ending 20 August – but the fall in the estimate is encouraging nevertheless.
“Uncertainty about the figures for the R number and the growth rate stems from the facts that they are estimated from a range of data sources, and that the estimation process uses mathematical models that, inevitably, cannot represent perfectly what’s going on in the country. Because of the uncertainty, the Government, rightly in my opinion, does not give a precise single estimate but instead gives a range of possible values into which it is likely that the true R number and the growth rate will fall. This week’s range for the R number, for the UK as a whole, is the same as last week, 0.9 to 1.1. If R is less than 1, the number of new cases is falling, and if R is greater than 1, it is increasing. The range includes values less and 1 and greater than 1, which indicates that it is not certain whether new cases are increasing or falling. The R number itself does not explicitly say how fast any increase or decrease might be, but the growth rate estimate does, and the range for that is -2% to +1% per day, indicating that the number of new cases could be falling by 2% every day, or rising by 1% every day, or anything in between. The true growth rate is more likely to be in the middle of that range that at either end. So it looks as if a slow fall is a bit more likely than a slow rise. It is reasonable to say that these numbers broadly match ONS numbers, in that both sets indicate that the rate of new cases nationally is roughly stable. The detailed ONS figures are (mostly) for England, and it’s important to point out that the Government published ranges of R numbers just for England, as well as for the UK as a whole. For England, the R number range is 0.9 to 1.1 – the upper end is a bit higher than last week when it was 1.0. However, this change of the end of the range does not mean that the R number has definitely increased for England, just that it might have increased. The growth rate range for England is the same as for the whole of the UK, -2% to +1% per day. Figures for the other UK countries are produced weekly by the administrations there. They have not changed much from last week, with moves in the direction of fewer cases in Scotland and in Wales. In Northern Ireland, there is more concern, because the range for the R number runs from 1.0 to 1.6.
“Because of the uncertainty in all these figures, we have to remain vigilant. But in any case, as the Government points out alongside the R number estimates, the national R numbers, or indeed the numbers for individual regions, do not form a good basis for deciding policy at this stage in the pandemic. That’s because the distribution of new cases is very patchy, because the overall numbers are relatively low. So there are outbreaks in some places, and when outbreaks occur, actions are being taken and the rates of infection in those places generally decrease again. It’s more important to keep local outbreaks in check than to worry unduly about whether the national R number is just above or just below 1.
“Because they are based on a range of data sources, including hospitalisations and deaths, the R number and growth rate estimates do involve a time delay after the initial infection. Therefore these figures cannot reflect the absolutely up-to-date position, and nor can the data from the ONS survey (because it takes time to do the tests and collate the results). The daily published figures for confirmed new cases are rather more up to date, but they are affected by quite large fluctuations from day to day in the numbers and type of people tested. Yesterday’s figure for confirmed new cases was higher than it had been for some time. That did not unduly concern me – it was only one day, the numbers fluctuate a lot, and one high figure doesn’t make a trend.”
ONS Infection Survey: https://www.ons.gov.uk/peoplepopulationandcommunity/healthandsocialcare/conditionsanddiseases/bulletins/coronaviruscovid19infectionsurveypilot/englandandwales28august2020
R number and growth rates: 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 Kevin McConway: “I am a member of the SMC Advisory Committee, but my quote above is in my capacity as a professional statistician.”
None others received.