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The government have released the latest statistics from the COVID-19 Test and Trace system.
Prof Kevin McConway, Emeritus Professor of Applied Statistics, The Open University, said:
“When these weekly Test and Trace statistics came out last week, I commented on the time it was taking between a new positive case of Covid-10 being identified and the contacts of that person being reached by the contact tracers and asked to self-isolate. It’s vital, not only that a big enough percentage of possibly infectious contacts are traced, but that the people who might have been infected are reached quickly enough to stop them passing the infection on further. There are several stages to go through before that can happen. The original infected person has to be tested, and their test results have to be produced and passed to the contact tracers. The contact tracers have to contact the infected person and ask about their potentially infectious contacts. Then they have to reach those contacts and ask them to self-isolate. All of these stages take time, and any delays can quickly add up.
“There’s a little good news about parts of the process in this week’s report. For the latest week (15-21 October), the median time between a person taking a test and the result being received has gone down a bit, compared to last week, for all the different types of testing considered. The median is the time within which half the test results are received. Last week, for the regional test sites the median was 46 hours, so the test results were received in less than 46 hours for half the tests that were done, and more than 46 hours for the other half. This week, that number has reduced to 39 hours, and there are broadly similar reductions for other types of test site. That indicates speedier work by the labs processing the tests, and the quicker the results are received, the quicker the rest of the contact tracing can happen. However, for all the types of test site where people are tested in person, the median times are still considerably longer than they were up to the end of September.
“The bad news on timings is that the times taken for most other stages of the contact tracing process have increased. For the latest week, only 45% of cases were reached by the contact tracers, and asked to provide information about their contacts, within 24 hours of their case being transferred to the contact tracing system. The previous week it was 54%, and in fact this week’s 45% figure is by some margin the lowest percentage to be reached within 24 hours in any week since the Test and Trace programme began. And then the time between a case being identified and passed to the contact tracers, and that person’s contacts being reached, has increased again. In the most recent week, only 29% of contacts were reached within 24 hours of the case that they contacted being passed to the tracing system. That’s down on the previous week, when it was 32%, and again this week’s figure is lower than the percentage for every week since Test and Trace began. (These timing statistics are for cases managed by the national system rather than local health protection teams – those local teams generally perform better, but they deal with under 3% of cases.)
“I’m sure these increased delays are because of the increased volume of cases and contacts that the system is having to deal with. The number of new positive cases in the most recent week was 126,000 in the most recent week, up 23% on the week before. The number of contacts to be traced was 285,000 in the most recent week, up 12% on the previous week. But last week I said that the performance really isn’t good enough, and this week it has got worse. This needs to be fixed urgently. The system needs to be able to cope with the number of new cases that are happening, and the indications are that it’s just not coping well enough. And numbers of new cases continue to increase.
“There’s not really much good news elsewhere in the statistics either, I’d say. The number of people testing positive has gone up, which can’t be good, though it went up more slowly over the most recent week than in late September and the start of October. That might just indicate a slowing in the rate at which the pandemic is spreading – but we can’t be sure of that by any means. The number of positive tests depends on the number of people tested, and also on which people are coming forward to be tested – where they live, what jobs they do, and so on. That can change over time, and that will affect the number of positive tests, and the percentage of tests that have a positive result. Much better indicators of the way the pandemic is developing come from surveys that test representative samples of the population, only for the purpose of tracking the pandemic. England is very lucky to have two different surveys of this sort running – the REACT-1 survey from Imperial College (from which the latest results were published earlier today), and the Office for National Statistics (ONS) Infection Survey, for which the latest results will be published tomorrow.
“One welcome feature in today’s Test and Trace statistics is that they have stopped referring to cases as being ‘complex’ or ‘non-complex’. Instead they are described as being ‘managed by local Health Protection Teams’, or ‘not managed by local Health Protection Teams’. That’s actually what ‘complex’ and ‘non-complex’ always meant, but those previous terms implied somehow that the whole contact tracing process would be more complex and difficult for cases managed by the local Health Protection Teams, which was never really the case.”
Prof David Heymann, Professor of Infectious Disease Epidemiology, London School of Hygiene & Tropical Medicine (LSHTM), said:
“Though it is useful to understand the number of contacts being identified – which varies depending on social interactions – and to understand how many of them have been followed up and are self-isolating, most epidemiologists believe that the most useful indicator of the effectiveness of contact tracing is the number of new cases that occur in persons who appear on contact tracing lists and are self-isolating.
“The fact that the time from testing to availability of results is decreasing will make contact tracing more effective in rapidly identifying contacts and decreasing transmission from them to others in the community and the best time lapse is minutes and hours rather than days.
Prof James Naismith FRS FRSE FMedSci, Director of the Rosalind Franklin Institute, and University of Oxford, said:
“The positivity rate has climbed, suggesting we are not doing enough testing. The REACT survey would indicate 1.5 million or more tests per day are needed for a 5 % positivity, the Nowcast at least 750 thousand
“Around 97, 000 (76 %) of people who tested positive were reached for details, less than half in 24 hrs. 81, 840 (2/3 of the positive tests) gave details and identified 284, 701 contacts.
“Of these contacts 172, 000 were reached (60 % of known contacts). Accounting for the fact 1/3 of positive tests were either not contacted or gave no details, suggest less half (around 40 %) of the contacts of the people who tested positive were reached.
“Of those reached over 70 % were in same household, so could have been reached without tracing. Less than 1/3 of contacts reached were reached within 24 hrs of the positive case being identified. Overall, this is less than 15 % of the contacts of the tested positive cases.
“The data from REACT and Nowcast, suggest less than half (possibly quite a lot less than half) of infected people are being identified by testing. This simply divides all the numbers above. This is why the system has not, is not and most likely will not halt the spread of the pandemic.”
https://www.gov.uk/government/publications/nhs-test-and-trace-england-and-coronavirus-testing-uk-statistics-15-october-to-21-october
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