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It has not yet begun, but the UK’s new coronavirus contact tracing plan has already hit a series of stumbling blocks. The devolved administrations have turned away from the NHS-developed contact tracing app with Northern Ireland working on its own app and Scotland as-yet refusing to endorse the NHS app for its own citizens. The first recruits to the government’s 21,000-person-strong “army” of contact tracers, meanwhile, have criticised the scheme’s inadequate and unclear training.
But the UK’s contract tracing plan has two more fundamental flaws that threaten to undermine its effectiveness. Without fixing these flaws, researchers – and people involved in the development of the contact tracing plan – worry that the effort will be fatally hamstrung.

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The first problem is within the contact tracing app developed by NHSX – a government unit set up to bring new technologies to the NHS. The app is unusual in that it does not send alerts based on confirmed cases of coronavirus. Instead, in its current iteration, it asks users to report whether they have coronavirus symptoms and if they do, an alert may be sent to other app users with whom they have been in contact. At the moment, this alert contains advice asking those contacts to pay close attention to whether they are developing symptoms, but it does not ask them to self-isolate.
This approach makes the UK something of an outlier compared to other countries. Proposed or active contact tracing apps in Germany, Australia, Austria, France, Iceland and Singapore all rely on testing, rather than symptoms. Of national apps where clear information is available, only China’s incorporates self-reported symptoms, although it also makes use of much more detailed information such as medical records, travel history and body temperature. The proposed UK app does not collect personally identifiable information or location data.
Self-reporting symptoms offer some advantages over waiting for test results. Contacts will be alerted more quickly, meaning that people potentially exposed to the virus can adjust their behaviour to reduce risk to other people. And with a disease that is thought to spread before symptoms are present, a speedy indication of whether someone is infected is vital. But an app that relies solely on self-reporting has serious limitations.
“If I get a message every two minutes because I was in contact with somebody who possibly might have the virus, what is that going to do to my behaviour? I’m going to start ignoring it,” says Caroline Wiertz, a professor at City, University of London’s Cass Business School and the author of a study that examined the factors that influence how likely people are to use the NHS app. Wiertz found that priority access to testing was the second-most important factor that would encourage people to download the app.

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Wiertz’s findings are echoed by Jonathan Montgomery, a professor of healthcare law at University College London and the chair of the ethics advisory board set up to oversee the development of the app. “[Ethics advisory board] members have voiced similar concerns and worried that false positive alerts could undermine trust in the app and cause undue stress to users,” Montgomery wrote in a letter to Matt Hancock on April 24, before the trial on the Isle of Wight was started. “We would also caution against proceeding with the app without widespread access to virological testing. It is our view that introducing widespread testing and incorporating this into the app as soon as reasonably possible would significantly increase both confidence in the app and its efficacy,” he wrote.
But public health experts are concerned that the app will rely on self-reporting because the government is not confident it can test widely and quickly enough to support a German-style app based on confirmed infections. “The correct way to do [contact tracing] was firstly not to stop on March 12 and secondly to plan it in advance of starting to lift social restriction,” says Gabriel Scally, professor of public health at the University of Bristol and a former regional director for public health.
So is the UK testing quickly and widely enough to run an effective contact tracing regime? This is still an open question. Scally says that results should be returned within two or three days to be most effective. This tallies with the coordinator of the UK’s testing programme, John Newton, who said at the government press conference on May 21 that although there is no hard limit for when test results should be returned by, the faster they are, the more effective contact tracing would be.
According to the Department for Health and Social Care (DHSC) 95 per cent of tests “across all settings” are processed within 48 hours. This was contradicted slightly at the May 21 press conference by Newton who said that the 48-hour figure was actually 90 per cent, with 50 per cent of tests being returned within 24 hours.

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But this doesn’t tell us how testing times vary according to the way the test is administered. On May 20, 128,340 tests were processed, which accounted for 67,681 people being tested. Of those people, 24,574 of them were classed as pillar one tests: people in healthcare settings or health and care workers. The remaining 43,107 were in pillar two: essential workers and their households, or those who meet the government criteria for testing.
The DHSC refused to confirm the average test processing time for pillar two tests, or to say whether it differed from the overall testing figure. The spokesperson said that while knowing the breakdown of testing times would be useful in principle, there were no plans to make that information publicly available.
Without knowing the timings of pillar two tests, it is impossible to say whether the UK is testing people quickly enough to support an effective contact tracing system. But anecdotal evidence suggests that people in pillar two are facing unworkably long waits for test results. One man tested on May 7 at the drive-through centre in Manchester’s Etihad stadium didn’t receive his result until May 16. Even then the result for himself and his daughter was labelled “unclear” – two of the thousands of tests that come back inconclusive, according to a report from Sky.
Other tests which WIRED has seen evidence of were also way outside the 48-hour window needed to make contact tracing as effective as possible. One woman tested on May 6 at a drive-through testing centre in Worcester waited six-and-a-half days for her negative result. Another woman who ordered a home test kit on May 18 did not receive the test until May 21. People who have had tests are told that results may take as long as five days to arrive.
While this is far from clear evidence that the UK’s testing is still too slow, it raises concerns that testing is currently still not at a level able to support contact tracing. As Scally notes, it is people who fall into pillar two – those being tested at home or at drive-through centres – who will likely form the bulk of those tested in a contact tracing programme.
Under pressure from local authorities to ramp up testing, the government is asking ten local authorities to develop local action plans that will help deal with outbreaks in schools, care homes and workplaces. A source involved in the plan told WIRED that this test would come ahead of the national rollout of the test and trace service, which is slated to be in place from June.
But the combination of a reliance on self-reported symptoms and unclear testing times may mean the plan faces an uphill struggle. The World Health Organisation (WHO) has said that a strong approach to testing will mean that countries see many, many more negative tests than positive. Countries with extensive testing have a positive test rate of fewer than 12 per cent, said Michael Ryan, executive director of the WHO Emergencies Program at a press conference on March 30. In the UK, the percentage of people tested who returned positive results is currently 11.9 per cent.
This poses a problem for an app reliant on self-reporting of symptoms. If nearly 90 per cent of people who had a test ended up being negative for the virus, what percentage of those who think they have symptoms will end up being wrong? “Unless they can link this to a really efficient testing process, it can’t work. And that’s the whole point. Right? It’s always tracing and testing. This is always mentioned together and there’s a reason for it,” says Wiertz.
Wiertz is worried that if it launched with just self-reporting, the app will quickly frustrate people who may receive frequent alerts but cannot be certain that they have actually been exposed to Covid-19. “I think you get one shot at it,” she says. She has raised her concerns with the Oxford epidemiologists who are advising the NHS on its app, but so far there is no indication that the government is planning on changing its approach.
Internal NHS documents previously seen by WIRED said developers were looking at a “lightweight new process for verifying clinical results” within the app. However, this has not been formally confirmed by the government or NHS.
Scally and Wiertz agree that without fast, widespread testing, a reliance on self-reporting alone may undermine the government’s contact tracing efforts. With the app still in testing on the Isle of Wight, public health officials are waiting to see whether the results of the test will lead to major changes before its rollout in June. Wiertz is hoping that the government will take heed of her study, and the examples set by other country’s apps. “I’m really hoping that they have realised with this piece of information and all the other pieces of information that they need to get the testing in place before they can launch the app,” she says.
Matt Reynolds is WIRED’s science editor. He tweets from @mattsreynolds1
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