About this tracker

  • The NHS Test and Trace (NHSTT) system aims to control the spread of COVID-19 in England by ensuring that people can be tested when necessary, and by identifying close contacts of people who have tested positive (positive cases) and asking them to self-isolate.
  • The government’s Scientific Advisory Group for Emergencies (SAGE) has recommended that at least 80% of close contacts of positive cases must be reached for the system to be effective.  
  • In this tracker, we monitor and reflect on the performance of NHSTT, analysing the latest statistics on the number of positive cases reached and the number of contacts who were asked to isolate each week since the launch of NHSTT on 28 May 2020.
  • The tracker will be updated every 2 weeks. It was last updated on 7 January 2021 with additional data covering 24–30 December 2020.

Key points: 24–30 December 2020

As the number of cases and contacts increase, there is some suggestion that testing may be struggling to keep pace.

  • There have been marked changes to NHS Test and Trace performance since we last updated on 3 December 2020.
  • The number of people testing positive is rising steeply, almost tripling in three weeks to 311,000 positive cases between 24–30 December. This is alongside a 30% drop in the number of people being tested this week compared to last, to 1.85m people.
  • As test demand increased in the first three weeks of December, the time taken to get results for PCR tests in the community started to increase markedly. For example, the median length of time for people to get a result from a regional test site rose from 21 hours to 38 hours. In the most recent week reported, the time taken for results has improved across all test routes alongside the fall in test demand, but is still not back to where it was three weeks before, which for regional test sites was 29 hours. It is crucial that people can get results quickly to reduce the amount of time between symptom onset and the start of contact tracing.
  • Contact tracing performance has remained fairly consistent over the month of December despite rising numbers of cases being handled. In the week starting 24 December, 270,000 people were transferred to the system, 229,000 (85%) were reached and 494,000 contacts were identified. This is nearly 300,000 more contacts than just three weeks before.
  • An impressive 92% of contacts were reached and asked to isolate, a consistent figure seen throughout December since NHS Test and Trace changed how they manage multiple contacts in the same household (since 27 November, a case can take responsibility for informing household contacts about their need to isolate rather than contact tracers phoning each contact individually).
  • Finally, after week-on-week improvements, the percentage of cases reached within 24 hours has dropped to 73% from 80% in the previous week. This has implications not only for the speed of identifying contacts, but also for local authority-led contact tracing systems that take on cases that the national team are unable to reach within 24 hours. The dip in performance may be because of having to adapt processes over the Christmas holiday period, and it will be important to monitor how performance here changes in the coming weeks.

Long read

NHS Test and Trace: the journey so far

About 16 mins to read

Long read

Launched at the end of May, NHS Test and Trace is not yet the ‘world-beating’ contact tracing...

Key points from previous weeks

  • The number of people testing positive has fallen by a third from two weeks ago, with 111,000 positive cases between 19–25 Nov.
  • The number of people getting tested has also reduced over this time period, which has coincided with improvements in the time taken to receive results. For example, now 72% of people using home test kits get a result within 48 hours compared to 57% the week before.
  • As the number of people testing positive has fallen, so have the number of cases being transferred to NHSTT. There were 116,000 cases transferred of which 99,000 were reached (85%), and 247,000 contacts identified.
  • While percentage of cases reached by NHSTT has stayed the same, the percentage of contacts reached has jumped to 73% from 61% the week before. This is because NHSTT has changed how they manage household contacts under 18. Instead of having to separately reach all contacts who are under 18 years, the parent or guardian can take responsibility. This makes sense and ensures that households receive fewer calls. Plus, the immediate impact of this change on performance suggests the change has been welcomed by households. The improvement in percentage of close contacts reached is entirely due to improvements in reaching household contacts. For non-household close contacts, the percentage reached remains at 64%.
  • And of course, being able to record reaching these household contacts at the same time as phoning the case has done wonders for the overall timeliness of contact tracing. The percentage of contacts reached within 24 hours of a case being identified has increased to 61% from 44% the week previously.
  • The system still needs to improve however. Underlying all this remains the fact that over 17,000 cases weren’t reached by NHSTT, and only around 60% of the contacts of identified cases are being reached (based on 85% of cases reached, and 73% of their identified contacts), still far from the 80% level recommended by SAGE.

  • After two weeks of improvements, NHS Test and Trace performance has stalled whilst the number of people testing positive continues to rise.
  • Nearly 157,000 cases were transferred to the system in the most recent week, up from 142,000 the week before. However, the number of contacts identified remained largely the same at around 314,000. This is because the number of contacts per case has fallen over the past few weeks, possibly a result of increased social restrictions.
  • The percentage of contacts reached by NHS Test and Trace remains just 61%, a figure that’s barely changed for the past five weeks. This means that optimistically, 51% of the contacts of known cases are being reached (based on 84.9% of cases reached and 60.5% of contacts), far lower than what is needed to meaningfully limit disease spread.
  • Finally, the data provided still don’t show the contribution of local contact tracing systems to overall NHS Test and Trace performance, and the updated local authority data highlight huge variation in the proportion of cases and contacts reached in different parts the country – the percentage of cases reached ranges between 71% and 93%, and for contacts it ranges between 49% and 68%.
  • Local contact tracing systems are being implemented across the country to work with NHS Test and Trace and reach cases the national team are unable to contact. As we move into winter, they are likely to play an important role in improving overall NHS Test and Trace performance, alongside ensuring that people who are identified as cases and contacts have adequate financial and practical support whilst isolating.

  • Between 22–28 October, nearly 140,000 cases were handled by NHS Test and Trace, 16% more than the previous week and a nine-fold increase since the start of September. Despite this rapid increase, the system has consistently been able to reach over 80% of cases, however the percentage of contacts reached stubbornly remains at 60%.
  • This means that whilst 115,000 cases and 196,000 contacts were reached and advised to isolate, over 24,000 cases and 131,000 contacts weren’t. And the system is still far from achieving the 80% of contacts needed for the effective system recommended by the government’s Scientific Advisory Group for Emergencies (SAGE).
  • Encouragingly, the time between taking a test and getting results is falling and the percentage of cases being contacted within 24 hours has increased to 67%. This is a significant improvement on just 44% the week before. The widespread use of rapid test kits may help to further improve the time it takes to receive test results, but this is still being piloted and not yet available across the country.  

  • The number of people testing positive keeps rising, up 12% from last week to over 100,000 this week for the first time. And of the 96,521 that were passed to NHSTT, call handlers were still able to reach 81% of cases.
  • But things are taking longer. The median length of time taken for people to receive test results for in-person tests (regional, local and mobile test sites) has jumped from 28 hours last week to 45 hours this week. The proportion of non-complex cases reached within 24 hours of being passed to NHSTT has fallen to 54% compared with 77% at the beginning of September (with implications for local contact tracing teams – see last week’s entry below). And the proportion of their contacts reached within 24 hours of the case being transferred to NHSTT is now just 32% compared with 52% back in early September.
  • And while the proportion of cases being reached remains high, the proportion of contacts reached has fallen for the fourth week in a row to 60% of all contacts. But rather than this being due to worsening call handler performance, it’s mainly a result of non-complex contacts (where there is a lower success rate of being reached compared with complex contacts) making up a higher proportion of all contacts this week compared to the week before.
  • The average number of contacts per case for the 76,096 non-complex cases transferred to NHSTT is the same as last week, but for the 1,796 complex cases, the average number of contacts has fallen from 29 per case three weeks ago to just seven per case this week. This may just be due to chance, but it also may represent a combination of better social distancing, more limited social mixing, and appropriate use of personal protective equipment (PPE) in care settings.

  • On 2 October, the national system identified an error in how pillar 2 cases are transferred to contact tracing. This meant that 15,841 cases (from 25 September to 2 October) that hadn’t previously been sent through to NHS Test and Trace (NHSTT) were transferred in bulk on 3 October. Therefore, this week’s data include 11,000 cases transferred to NHSTT that would have ordinarily been dealt with the previous week.
  • This week the percentage of cases reached increased from 75% to 77%, and the percentage of cases providing details of contacts also rose from 83% to 85%, its highest since NHSTT began. This shows a slight improvement but doesn’t tell the whole story.
  • There were still 20,000 cases that weren’t contacted by NHSTT, and of those cases providing details of contacts, the average number of contacts per case has dropped significantly. This could be due to several factors including people not mixing as much due to increased social restrictions. Correspondingly, the percentage of all contacts that are from the same household as the case has been rising for four weeks in a row, from 57% in the first week of September to 66% in the most recent week.
  • Local contact tracing systems are being set up across the country - around half of local authorities now have one in place. Generally, these local systems follow up local cases that the national team hasn’t reached within the first 24 hours of being transferred to NHSTT. Their workload in recent weeks has not only been affected by rising case numbers, but also by significant delays in how long the national team takes to reach cases. The percentage of cases reached within 24 hours has fallen for four successive weeks, and now stands at just 56% of all cases transferred, down from 77% in the first week of September.
  • The percentage of contacts of non-complex cases that NHSTT reaches is also falling, and is now just 58% compared with 64% two weeks ago. This may partly be down to difficulties in reaching contacts from cases whose transfer to NHSTT was delayed, but when factoring in evidence that as little as 11% of contacts may actually comply with isolation rules, the implications for containing transmission are significant. These issues are exacerbated by how long it’s now taking for NHSTT to reach contacts and advise them to self-isolate. The proportion of close contacts reached within 24 hours of either the contact or the case first being identified is now at an all-time low of 61% and 39% respectively.

Useful definitions

  • Cases are people who have had a positive antigen swab test.
  • Cases managed by Public Health England local health protection teams (HPTs) are those linked to outbreaks, for example someone who works at or recently visited a hospital or care home. These cases were previously known as complex cases. All other cases are not managed by local HPTs and were previously known as non-complex cases.
  • Close contacts are defined as anyone who a case has had face-to-face contact with (within 1 metre), spent more than 15 minutes within 2 metres of, travelled with in a car, or sat close to on a plane.

Further reading

Long read

NHS Test and Trace: the journey so far

About 16 mins to read

Long read

Launched at the end of May, NHS Test and Trace is not yet the ‘world-beating’ contact tracing...

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A timeline to 7 December 2020 of national policy and health system responses to COVID-19 in England.

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