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

“Today’s publication from ONS (based on data to the end of last week) is very encouraging. The prevalence of the virus has continued to drop, albeit it slowly in all UK nations and essentially all regions. It is safe to conclude that the re-opening we have seen this far, has not triggered a resurgence. The vaccine campaign has clearly had its desired effect, with infection rates lowest in the over 50’s. The decrease in prevalence in children is good news, the less virus in the UK the less chance for variants.

“I continue to support the government’s staged re-opening. There remains a risk from new variants, but the UK’s expertise in sequencing is world leading so we can be confident we will know in good time if this poses a threat. We can do all do our bit to stop the virus and its variants: mask indoors, use the outdoors in the warmer weather, wash our hands, isolate if sick and enrol in the at home testing scheme.

“It is beyond doubt that vaccines are the only humane way out the pandemic. I am delighted to see the vaccination progress in the EU and USA.

“The scenes from India on television are heart breaking and my sympathy is for the families left bereft. What is happening in India is stark illustration of the havoc that rapid spread of the virus does; healthcare overwhelmed and vulnerable people suffocating to death in ambulances waiting for help. This might be an appropriate point for those who so blithely advocated ending the UK lockdown in the autumn / winter to reconsider their analysis. The UK has avoided the fate that has befallen India (and many other countries who we do not see on our TV) because of the action of our governments and every one of us who wore a mask, distanced, washed our hands and isolated when sick. Vaccination now means that we will not ever see such scenes from covid19 here.

“We are however not safe until the virus is under control everywhere. Richer countries must, for both their own sake and for common humanity, do all they can to increase the supply of vaccines to less well-off countries. I would urge richer countries to continue to support the development of new medicines that can treat covid19.”


Prof Oliver Johnson, Professor of Information Theory, School of Mathematics, University of Bristol, said:

“This latest data suggests that coronavirus infections continue to fall, despite the relaxation of some lockdown measures. Although it is too early to draw conclusions from this survey about the effect of the 12th April relaxations, it appears that the Easter break and safe outdoor socialising have helped to reduce cases reported this week. It is particularly encouraging to see that prevalence is particularly low among the most vulnerable age groups, and that levels are consistently low across all four home nations and all regions of England.”


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

“Today’s regular bulletin on the ONS Covid-19 Infection Survey (CIS) gives more, pretty well unadulterated, good news. On prevalence, the estimated percentage of people in the community population who would test positive for the virus that can cause Covid-19, the data now go up to the week from 10 to 16 April. That week includes step 2 of the roadmap out of lockdown in England, with non-essential shops, gyms, hairdressers, out-of-doors catering and pubs, and so on, being allowed to reopen on 12 April, and many schools also going back after the Easter holidays then. It’s a bit early for any increases in infection from those changes to show up clearly in the data anyway – but it’s still good news that that hasn’t happened. Instead, ONS estimate that the percentage who would test positive continued to decrease in England, Wales and Scotland. In Wales, they conclude that the percentage testing positive remained level – but the positivity rate was already lowest of all four countries in Wales, and that’s still the case for the most recent week.

“The falls in positivity rates in the other UK countries than Wales, and the inevitable statistical uncertainty in estimating these rates from doing swab tests on a sample of people, mean that we can’t be completely confident that the rates do differ at all between the four countries. The central ONS estimates are that 1 in 610 would test positive in England, 1 in 840 in Wales, 1 in 660 in Northern Ireland, and 1 in 560 in Scotland. But there’s a lot of statistical uncertainty, particularly in the smaller countries. In Northern Ireland, for instance, the margin of error around the main 1 in 660 estimate goes from 1 in 330 to 1 in 1,640. That’s a big range – but even if the rate were 1 in 330, that’s really pretty low. To give an idea of the size of the reduction in people who would test positive in the most recent two weeks, the total of the ONS estimates of the number of people in the four UK countries who would test positive for the latest week, ending 16 April, is 105,700. The week before, ending 10 April (the ONS weeks do not always end on exactly the same day of the week), that figure was 129,000. So it fell by 18% in a week. That’s pretty substantial, particularly considering that lockdowns are being relaxed.

“One note of caution is that though the rates of testing positive in England and Wales are now down to the levels of early to mid-September, very far below the rates in the later autumn and the winter, they are still between two and three times as high as they were last August. (I can’t make that comparison for Northern Ireland or Scotland, because the CIS hasn’t been carried out there for so long.) So far, good news on effectiveness of vaccines means that concern about the effect of infections in individuals and the NHS is considerably smaller than it used to be – but a lot of people are still not vaccinated, and we do need to keep looking carefully at the data as we come more and more out of lockdown restrictions.

“ONS also give estimates from the CIS for positivity rates in the English regions, and in different age groups in England. Again, though, there is quite a lot of statistical uncertainty involved in those estimates, because the number of people swabbed in the survey for a single age group or a single region is obviously much smaller than for the whole country. ONS rightly warn against over-interpreting fairly small trends and differences in regional and age group estimates. On regions, though, the news is again pretty good. ONS consider that positivity rates are decreasing in five of the nine regions of England (North East, North West, Yorkshire and The Humber, East Midlands and London), and that the trend is uncertain in the others (West Midlands, South East, East of England, South West) – so they do not think there is clear evidence of increase in any region. There’s really no absolutely solid evidence that infection levels differ between regions, though it certainly looks as if they are probably higher in the North West than in the East of England and the South West. But regional differences do look smaller than they were when overall infection rates were higher, earlier in the year. With infection levels generally this low, I’d expect the picture to be dominated by outbreaks in limited geographical areas, rather than being a feature of whole regions.

“In terms of age groups in England, ONS consider that positivity rates have been falling in children of primary school age or younger, and in people aged over 35. The trends in people in the age groups between are unclear, ONS say. The differences between age groups are often too small to provide a clear statistical picture, but positivity rates do look to be highest in those of secondary school age, and lowest in those aged 50 and over. But the margins of error for most of these age groups are pretty wide.

“ONS also estimate the rate of new infections in each of the four UK countries. This is different from the estimates of the numbers who would test positive, because that would include people who have been infected for some time as well as new infections. The latest estimates for the rate of new infections are for the week ending 9 April, so a week earlier than the positivity estimates, because the data take longer to process to an acceptable level of accuracy. There’s good news here too, although the rates are so low that trends are pretty difficult to determine. ONS are estimating 8,200 new cases a day in total across all the UK countries for that week, compared to 12,380 the previous week. That’s a fall of about a third in a week – again pretty substantial, though the detailed estimates can’t be very certain. ONS consider that new cases are falling in England and in Scotland, but that they can’t be sure of the trend in Wales or in Northern Ireland.



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



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.


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