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expert reaction to latest Test and Trace Figures for England for the week 1 to 7 October

The government have released the latest COVID-19 test and trace figures for England.


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

“The good news is that the number of tests being done has gone up, and, on many measures, the time taken to get test results through has gone down a small amount. More people are being transferred to the Test and Trace system after testing positive, and the percentage of those who are actually reached by the tracers has increased slightly (though is still probably too low).

“The quite bad news is that the number of positive test results has gone up quite a lot since the previous week. This isn’t really news, though, given all the other recent data that have showed increases. It’s also not a particularly reliable measure of the spread of the infections, since the number of positive tests will depend on who’s being tested, how many people are being tested, where tests are carried out, and so on. More accurate information will, as usual, come from the ONS Infection Survey report tomorrow.

“The very bad news is that the percentage of contacts of positive cases who are reached by the contact tracers and advised to self-isolate has fallen quite a lot, and the percentage who are reached within 24 hours of the positive case being identified has fallen even more. It’s now under 40%. Arguably it’s never really been high enough, but it has fallen considerably since early September. If contact tracing can’t get in touch with contacts quickly, then any contact who have been infected may be walking around for days unaware that they have been in contact with an infected person and possibly passing the infection on further. This needs to be fixed.”


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

“Of the 89, 874 people who tested positive this week, roughly 77, 000 entered contact tracing. I have excluded 11, 000 from the previous week who were traced this week. 

“SAGE has described the system as of “marginal benefit”. 

“Simply looking at the increase in the number of cases, is proof that the system has not succeeded. 

“The reasons are not hard to see.

“First, the 89, 874 is an underestimate of the actual number of cases, ONS and REACT data suggest testing is missing a significant number of infected people. Those do not know about we cannot trace.

“Second, we reach only 75 % of those who test positive. (67, 511 people)

“Third, on average each person identifies three close contacts, two of which they live with. We have no idea if this is accurate or not, since no effort has been made to find out. The point here is that this is the whole gain of the system the non-household contacts.

“Fourth We only reach around 2/3 of the identified contacts. (136, 000 out of 216, 000)

“Fifth The Royal Society emphasised speed, but the system is still too slow with only 60 % of close contacts being reached in 24 hrs

“Six We do not know how effective the isolation is. Some estimates suggest as low as 20 %

“ONS data suggest less than half of infected people are entering the testing system

“So for 100 people who are infected, only 50 are tested positive, only 75 close contacts are reached and asked to self isolate. Only 25 of these people don’t live with the person who tested positive, less than 14 of this group are reached within 24 hrs, less than 5 of them might isolate.

“I very much doubt the system can recover and run effectively in a timely manner. It will be almost impossible to fix it with cases rising, more likely it will become increasingly irrelevant but unfortunately increasingly costly.

“Even if cases were lower, it is not clear we have learned enough to even know how to make an effective system. The system is a perfect example of “Sounds simple, surely anyone can do it”. Getting a useful system was always incredibly hard. It needed relentless political focus and the right sort of expertise. Even then it might have failed given the time pressure. Without them it was certainly going to fail. I fear we delude ourselves to promise hard work or new faces will solve it.”


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 the Advisory Committee, but my quote above is in my capacity as a professional statistician.”

None others received.

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