July 2, 2021

expert reaction to latest data from the ONS infection survey

The Office for National Statistics (ONS) have released the latest data from their COVID-19 Infection Survey.

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

“The latest results from the ONS Covid-19 Infection Survey (CIS) take the data up to the week 20-26 June. As always, the results come from a survey of a representative sample of the community populations of the four UK countries. As such, they aren’t affected by biases that might occur with the counts of new confirmed cases on the dashboard at coronavirus.data.gov.uk, if the type and numbers of people being tested happen to change.

“This week’s CIS figures don’t make very comfortable reading, generally. The dominance of the Delta variant in England, Wales and Scotland continues to increase, though it is still not dominant in Northern Ireland. ONS identify increasing trends in the numbers of people who would test positive for the virus in England, Wales and Scotland, though they say that the trend is uncertain in Northern Ireland. (It is more difficult to estimate the trend in the smaller UK countries from the CIS, because the numbers of people swabbed for the survey are lower there, so that the statistical uncertainty is greater than for England.) The rate of increase of infections is fastest in Scotland, though it is fairly rapid in England and in Wales too. ONS also estimate that the numbers testing positive have been increasing in all the English regions, and in almost all the age groups that that they use for their analysis in England.

“One very important reason to be positive doesn’t, however, show up in the CIS data at all, because these weekly CIS bulletins only estimate levels of infection, and not of hospitalisations or deaths. We know that vaccines have not entirely removed the link between infections and hospitalisations or deaths, but they have certainly weakened it a great deal. So the CIS data on infection provides only one side of the picture. If infections were rising at the current rate and we hadn’t had all the vaccinations that we’ve had, I’d be seriously alarmed. As it is, well, I’d be much happier if infections weren’t rising so fast, but I’m not hugely concerned about the UK position at present – not yet anyway.

“The central ONS official estimate of the number of people infected across the UK in the latest week is 256,400, which is 67% higher than last week’s total. ONS state that their ‘modelled estimates’ are more appropriate for measuring trends in positivity levels. In England, those figures went up by just under half in a week. If they continue to increase at that rate, the numbers of people who would test positive would double in a little under two weeks. The rate of increase is somewhat higher in Scotland, and a little lower in Wales, with a doubling time of about a week and a half in Scotland and a little over two weeks in Wales. The pattern in Northern Ireland is less clear and rather more complicated, and I don’t think it makes much sense to think in terms of doubling times there (as it is not even clear whether infections are increasing or decreasing).

“The rate of increase (or decrease) doesn’t tell us what the actual levels of infection are, just how they are changing. Those numbers of infected people, or to be precise of people who would test positive on a PCR test for the virus, do still differ quite a lot between the UK countries, In England, ONS estimate that 1 in 260 of the community population would test positive, with a margin of error from 1 in 230 to 1 in 290. Last week’s estimate was 1 in 440. The estimates for Scotland, Wales, and Northern Ireland are, respectively, 1 in 150, 1 in 450, and 1 in 670 (with wider margins of error than in England because of the smaller sample sizes). Despite the increases, these figures are still well below the infection levels at the height of the second wave of the pandemic early this year, except in Scotland. In England, the current level of infection is about what it was at the start of March this year, or before that in late September 2020. In Wales the current level is around where it was in mid-March this year or, again, late September 2020. In Scotland the current level is about where it was in late January this year, though the peak of infections early this year was not as marked in Scotland as it was in the other UK countries. In Northern Ireland current numbers are somewhere around the level of mid-April, so very much lower than the high levels at the turn of the year. (In Scotland and Northern Ireland, it isn’t possible to make comparisons with early Autumn levels from 2020 because the CIS was not running in those countries at that time.)

“For the latest week or two, ONS report that the percentage of people testing positive has increased in all nine regions of England, though the trends are less clear in the East of England and the South West. The numbers of people that would test positive do vary quite considerably from region to region, with the highest numbers in the North East and the North West (1 in 100 and 1 in 110 respectively, though the smaller sample sizes mean that there are quite wide margins of error). In the regions of the south of England, numbers are lower (1 in 340 in London, and lower still in the other regions, between 1 in 500 in the South West and 1 in 640 in the South East, again with rather wide margins of error). In age groups in England, ONS report an increasing trend in infections in all age groups except those over 70. However, numbers testing positive do continue to vary a lot according to age. In the age group from school year 12 (16/17 years old) to age 24, ONS estimate that 1 in 70 people would test positive (with a margin of error from 1 in 50 to 1 in 100). Even allowing for the statistical uncertainty, that’s considerably higher than all the other age groups. Infection rates in the age groups over 35 remain relatively low, though they are increasing except for the over 70s. For the 70+ group, ONS estimate that only 1 in 1,030 would test positive.

“This pattern by age group emphasises the importance of vaccination. I don’t think vaccination is the only reason that infection rates are so much lower in the older age groups than the younger groups, but it must be an important part of the reason. On the whole, though infection rates increased in recent weeks in nearly all age groups, they have been increasing more slowly in the groups where vaccinations levels are highest, particularly in the groups where many people have had both doses. I hope, and expect, that as more of the youngest adults have at least one vaccine dose, and more middle-aged and younger people have both doses, that the numbers of people who would test positive will increase more slowly. If that doesn’t happen, and infections do continue to double in something like every two weeks, it won’t take all that many weeks until infections are back at the sort of levels we’ve seen in previous peaks – so we can’t stop being vigilant, particularly as and when more restrictions are removed.”

Prof James Naismith, Director of the Rosalind Franklin Institute, and University of Oxford, said:

“Today’s release covering testing data for the week ending 26th June is unsettling.

“We are firmly now in a third wave of cases. The prevalence in Scotland is estimated to be around 7 people per thousand, England around 4 per thousand. Given the continuing rise in cases revealed by daily test numbers, we can guess Scotland is reaching 1 % infection rate. Wales has also seen an uptick in cases. Some age groups are already over 1 % infection.  The Prime Minister’s and Parliament’s decision to delay unlocking for a month has been validated; more people have been vaccinated and delta has been slowed.

“Without vaccines, however even these numbers and this trajectory would spell disaster. The delta variant is still growing despite track and trace, despite testing, despite restriction and despite masking. The Government commitment to release restrictions on July 19th, means the rate of growth of infections will accelerate. It seems now unavoidable that delta will sweep through the unvaccinated (mainly young). Although young people are at much less risk, it’s not zero. A wave on the scale of what now seems likely will result in lives being blighted. One view, which I have disagreed with was since covid19 “mainly” affects old people it does not matter so much. This seems to have been replaced with, now the old are vaccinated, the young can get on with it which I find equally wrong. Only young children seem to be at almost zero risk. In any event, we are conducting the experiment so we will undoubtably know the truth of this.

“I would urge all those who are not fully vaccinated, to get doubly vaccinated as soon as they can, especially those who are in the most vulnerable groups. For those who have had very weak immune responses to the vaccine; I would suggest they shield themselves if possible even more carefully than before. If you are interacting with the vulnerable, then your wearing of a mask will protect them to some level. Unless you are lucky or extremely careful we are all going to be exposed to delta.

“Increasing vaccination and time will end the delta wave in the UK.

“Since track and trace has failed to hold back delta (or before that alpha) in Scotland and in the UK, it is unclear whether its retention has any value to public health, particularly given current vaccination rates.

“Although we focus on the UK our point of maximum danger has probably passed, although I remain very concerned about the harm for younger people.

“Delta is going to sweep through the EU in much the same way as here, fortunately they too are vaccinating at a very fast rate. They like the UK are probably just past the point of maximum danger but summer will be rough.

“With so few people in developing countries vaccinated, their point of maximum danger is ahead. Once delta gets going it will overwhelm health care systems very rapidly unless vaccination improves. Overwhelming health systems will lead to disproportionate rise in deaths as oxygen runs out, health care professionals are knocked out and other care halted. More thought needs given to whether vaccinating young children in the rich world is as important and ethically justified as vaccinating key workers and the most vulnerable in developing countries.

https://www.ons.gov.uk/releases/coronaviruscovid19infectionsurveyuk2july2021

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 Trustee of the SMC and a member of its Advisory Committee.  I am also a member of the Public Data Advisory Group, which provides expert advice to the Cabinet Office on aspects of public understanding of data during the pandemic.  My quote above is in my capacity as an independent professional statistician.”

None others received.