New NHS tracing app right just ‘half of time’
Pilot studies of phone warning system come after months of delays including dumping of original app
THE NHS contact tracing app being developed is so far only right half of the time – with a “false positive” rate of 45 per cent, trial data suggest.
The Government today announces pilots of a new contact tracing app for Covid, which will be tested in the Isle of Wight and the London borough of Newham.
It follows months of delays, after previous attempts to develop an app were abandoned when it was found to be too inaccurate.
Officials said they hoped the new app, being developed with Apple and Google, would improve its performance levels.
The system, already used in several countries across the world, uses Bluetooth to keep an anonymous log when phones are near each other. The new app will also allow users to scan Quick Response codes at pubs and restaurants so patrons can be alerted if other customers test positive.
It will also alert users to their general risk levels, depending on the postcode they are in and its level of infection. And if a user is told to self-isolate, a timer feature will help count down that period.
The app is supposed to alert users, and tell them to self-isolate for 14 days, if they have been within two metres of someone who later tested positive for Covid for at least 15 minutes. Testing of the technology so far has found that for every 10 cases which should be detected seven are detected successfully, while three are missed. But calculations from 100,000 simulations also found a “false positive” rate of 45 per cent – meaning almost half of all the cases being identified as close contacts do not actually fulfil the criteria.
Health officials said they hoped to improve on the accuracy on this in the next update to the technology, next month.
They said some of those which were counted as “false positives” could involve people who had been in fairly close contact with Covid cases, though further than two metres away.
Prof Christophe Fraser, from Oxford University’s Big Data Institute, an adviser to the NHS, said: “At the moment contact tracing is based on getting people to recall who they have been close to for 15 minutes. This [level of performance] is way better than that.”
Originally, ministers promised that a contact tracing app would be available in May. But the NHS version was repeatedly delayed, and finally ditched in June. Prof Fraser said improvements in contact tracing were vital to ensure the safe reopening of schools.
Baroness Harding of Winscombe, executive chairman of the NHS Test and Trace programme, said: “There is no silver bullet when it comes to tackling coronavirus.”
A Department of Health and Social Care spokesperson said: “Everyone receiving notifications that they have been close to a positive case is at risk of catching the virus – it would be irresponsible to suggest otherwise. They should take action, self-isolate and get tested.”