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expert reaction to updated statistics from the NHS Test and Trace service in England

The Department of Health & Social Care (DHSC) have published* updated statistics from the NHS Test and Trace service in England, covering the period 28th May to 10th June 2020.


Prof Keith Neal, Emeritus Professor of the Epidemiology of Infectious Diseases, University of Nottingham, said:

“Test, track and isolate is only one part of the control strategy. Percentage results are very similar to the week before. Over 90% of identified contacts have been contacted and asked to isolate. This is very good.

“About 1 in 4 known positives were unable to be contacted. Given that contact details have to be given to order a test, to be given details of where and when to get tested and then the result this figure remains a surprise and needs looking into. These cases could be part of small outbreaks and already in the system. If they are refusing to co-operate this is a potentially serious and very selfish attitude.

“We are still diagnosing fewer people with COVID-19 than current surveillance suggests. It is important that people who might have COVID-19 get tested so we can stop chains of spread. There is only so much the government can do. This is a public health crisis and the public need to play their part in stopping the disease.

“Lifting lockdown restrictions does not come without some risks. Currently most of Europe is at a lower level of restrictions than the UK and they have not seen cases rise. Either the UK is fundamentally different (which would help explain our high number of cases) or following Europe’s lifting of restrictions should not pose any major difficulties. Contact tracing allows us to get to less restrictions sooner.”


Prof Sheila Bird, former Programme Leader, MRC Biostatistics Unit, University of Cambridge, said:

“The Test & Trace scheme’s performance has been steady over its initial two weeks in terms of: a) the proportion of referred cases who are reached (73%, or 10,192/14,045); and b) the timeliness of reaching 7,964 non-complex cases, of whom 77% (6,097) were reached within 24 hours. Complex cases (which must by subtraction be 2,228) would seem to be 22% of those reached: it is these complex cases who are escalated to local health protection teams. Information on timeliness is not presented for this more complex task.

“However, the number of persons identified as recent close contacts does include complex cases: over two weeks the total was 96,746, of whom 90.6% (that is 87,639 close contacts) were reached and asked to self-isolate. Test and Trace works on trust that self-isolation is adhered to.

“The final information on timeliness of contact-tracing refers to non-complex cases, for whom 9,997 close contacts were reached, 8,530 of them (85%) within 24 hours.

“By subtraction, I deduce that the remainder of the identified close contacts who were asked to self-isolate (that is 77,642 persons) were identified by the 2,228 reached complex cases. Hence, on average, 35 identified close contacts were asked to self-isolate per reached complex case versus a mean of 1.26 identified close contacts per reached non-complex case. As yet, timeliness information is available only in respect of non-complex cases.

“Finally, the number of referred cases reduced by 27% from 8,096 during the period 28 May-3 June to 5,948 during the period 4-10 June, which is consistent with the ONS Infection Survey’s information on the reducing incidence of new infections. The first week included 1,434 reached complex cases who identified 41,667 close contacts who were asked to self-isolate (mean of 29 per reached complex case in week 1). The second week included only 794 reached complex cases, but they seem to have identified 35,975 close contacts who were asked to self-isolate (mean of 45 per reached complex case in week 2).

“As always, the devil is in the detail – are complex index cases doing better at identifying close contacts or, as we release from lockdown, should we indeed expect that the mean number of identified close contacts for complex cases will increase.”


Prof James Naismith FRS FMedSci, Director, Rosalind Franklin Institute, said:

“We are seeing the test and trace system in its early days. The system depends on widespread public support. A robust system is one (and only one) component required to avoid a second wave. Today’s numbers report marginal changes (in the right direction) compared to last week but I note that as the number of cases decreases, the system will be less stressed. I was encouraged to see the commitment to measure the speed of the journey, including testing time. This is the key parameter – we need to isolate people before they infect others.

“I would urge that thought is given to supporting people (financially and socially), who are being asked to isolate. Isolation must never be seen as a punishment or be a heavy burden. We have to accept that some uninfected people will be asked to isolate to ensure we catch as close as possible to all infected people; I would suggest that efforts are made to make sure the number of uninfected people isolated is minimised and the time they are isolated for is minimised.”


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


Declared interests

None received.

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