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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:

“The data released today covering the week ending 5th June show continuing growth in the number of cases.  Given Scotland and England have similar prevalence of the highly infectious delta variant it would be interesting to hear the scientific advisory committee member’s views on the basis behind their different approaches to crowds around the euro 2020 events.  Such large events clearly present a significant risk of sudden increase in spread.

“The good news in the ONS data is that the infection rise has been confined to the lower risk younger groups.  Lower risk is not no risk, long covid in young people is very serious.  This pattern is what one expects from the U.K. vaccination strategy, a word of caution is that it was also the pattern we saw with the Alpha variant which spread in the young first.

“If we remove restrictions and the delta doubling time drops to 4 days or less, then the number of cases will get very large very quickly.  In 20 days, we could hit 100, 000 cases.

“I believe we should wait for all the data before deciding what to do.  The red flag is hospital admissions in areas with cases that were high 10 days ago.  Let’s see this weekend if there is evidence of exponential growth, vaccine evasion and the most serious illness.  If so I would pause opening.

“What is certain is the delta variant will find those not immune to it.  It is critically important to doubly vaccinate those most at risk (older, poorer and ethnic minorities).”


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

“This week’s ONS release on their admirable Covid-19 Infection Survey (CIS) takes the data forward to the week 30 May to 5 June.  The news isn’t wonderful.  ONS estimate that the number of people that would test positive for the virus than can cause Covid-19 continued to increase in England, in Scotland, and in Wales over the two weeks up to June 5.  The trend in the latest week, however, isn’t clear in Scotland or Wales, and the overall recent trend in Northern Ireland isn’t clear, say ONS.  The rate of testing positive is still considerably less in Wales (estimated 1 in 1,300) than in England or Scotland (1 in 560 and 1 in 540 respectively), with Northern Ireland somewhere between (1 in 700).

“But we’ve got to keep a sense of perspective.  It would be much more comfortable if the infection rates weren’t increasing, but we already knew that they were very likely to be increasing, because of the increase in new confirmed cases that we’ve been seeing on the dashboard at, and this is linked to rise in cases of the Delta variant.  However, the increase in the ONS estimates this week is considerably less than last week, when the estimated numbers who would test positive across the UK went up by about two thirds compared to the week before.  For the latest week (ending 5 June) week, the overall number is about 13% up on the week before, so a considerably smaller increase.  The fact that the increase seems to be smaller, together with the statistical uncertainty of the survey results because infection rates are still low relative to that they were earlier this year, is the reason that ONS can’t be sure of the direction of the trend in the most recent week, except in England where the number of people swabbed for the CIS is relatively large.  The fact that the increase is smaller than the week before is a ground for a little hope.

“Infection rates in all four UK countries for the most recent week are roughly where they were in mid-April, so far, far lower than they were back in January and February, though of course in mid-April rates were coming down, and now they are going up.  Any increase is potentially concerning, even if it looks quite small, because infections in epidemics tend to grow by a fixed proportion every week if they are unchecked.  If that continues (and that’s a very big If), a small increase in numbers of people infected between last week could turn into a large increase in not too many weeks.

“Currently, over the past month, the estimated numbers who would test positive in England from the CIS have been growing by roughly 3% a day, so that (roughly) if 100 people would test positive today, 103 would test positive tomorrow.  That does roughly match the rate of increase that we’ve seen in new cases in England on the dashboard at – though it’s important to remember that the dashboard figures could be affected by biases because of changes in the numbers and type of people coming forward for testing.  That’s why confirmation from the CIS, which isn’t subject to those biases, is crucial.  If infections are increasing at 3% a day, and that continues over time, they will double every three weeks, very roughly.  Currently the 7-day average number of daily new cases in the UK on the dashboard is just less than 5,000.  If that 3% a day increase continues, that would be about 10,000 a day in three weeks from now, 20,000 a day in six weeks, and so on.  We’d be back to late February levels in six weeks.  But we absolutely don’t know that the growth will continue at 3% a day.  Continuing increases in vaccination will slow it down, but removing of restrictions on contact will tend to speed it up, and it’s difficult to predict how these things will balance out.

“The latest range for the daily growth rate in infections in England, from SAGE, is 3% to 6% a day – the figure of 3% that I’ve used in my calculations is at the bottom of that range.  As usual, though, SAGE mention that their ranges for the growth rate and for R represent the transmission of the infection two to three weeks ago, when the rate of increase in the CIS estimates was rather higher than it is now.  (A growth rate of 6% a day would mean, if it continued, that new infections would double every week and a half.)  Perhaps if SAGE could estimate the R number and growth rate on the basis of transmission of the infection now, they would be a little smaller than their latest published figures (which have a range of 1.2 to 1.4 for the R number in England, higher at both ends than last week’s range) – but I can’t be sure of that at all.

“What we also don’t know is how serious those new infections will be, if the numbers do keep going up.  Infections continue to be considerably more frequent in younger age groups, according to the CIS and other data sources.  In England, according to the CIS, about 1 in 1,330 people aged 70 and over would test positive, and about 1 in 740 of those between 50 and 69 years old.  That’s a lot lower than the England average of 1 in 560.  It’s lower still than that for children in school years 7 to 11 (secondary school up to about age 16), where the rate is 1 in 210, or for young adults between school year 12 and age 24, where it’s 1 in 240.  Infections were always relatively high in those age groups, but infections are becoming more concentrated there.  People in those younger age groups are much less likely to become seriously ill from Covid-19, if they get infected, than are people in their 50s or older.  Also most people in the older age groups have been vaccinated, often with two doses now, so that even if they are unlucky enough to become infected, the chance of being seriously ill with Covid-19 is considerably less.  So, as infections rise, the way that serious illness, hospital admission and deaths might rise will be different from how things would have worked last year.  That’s a positive aspect, though there’s uncertainty about the details.

“The relatively new Delta variant does continue to be concerning, partly because there are still things about it that we don’t know very well.  These CIS results indicate that positive tests that are not compatible with the previously dominant Alpha (‘Kent’) variant have been rising quite fast, and the great majority of those are probably the Delta variant.  There are now considerably more probable Delta infections than Alpha infections, though the CIS figures haven’t reached the level of 91% Delta that was announced yesterday by Matt Hancock (on the basis of different data).  PHE have published estimates of the effectiveness of the vaccines in preventing symptomatic Covid-19 in infections with the Delta variant, but not yet (as far as I’m aware) of their effectiveness against severe illness or hospitalisation.  The problem here is that symptomatic Covid-19 could be anything between a mild fever or persistent cough and struggling for breath in intensive care.  If (as seems increasingly likely) there’s an extension of restrictions in England beyond 21 June, that will buy time to find out more about vaccine effectiveness against serious illness – and, more importantly, it would allow time for more people to be vaccinated, with one dose or (ideally) two.  The data so far do indicate that having two doses is particularly important for effectiveness against the Delta variant.”



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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