NHS ‘improves accuracy’ of contact-tracing app as downloads near 20 million

Update will end ‘ghost notifications’, government claims
Danny Lawson/PA Wire/PA Images

By Sam Trendall

03 Nov 2020

An update to the NHS COVID-19 contact-tracing app will make the technology “more accurate” the government has claimed.

 The app was launched nationally last month and has since been downloaded 19 million times, which the Department of Health and Social Care indicated equates to 40% of all adult smartphone users. 

An update that came into effect yesterday is designed to improve the accuracy with which the program can, using a phone’s Bluetooth technology, estimate the distance between users. This, alongside infectiousness, is used to calculate which users are told to self-isolate.

The improved accuracy in measuring distance means that the “risk threshold” at which users are notified that they should isolate has been lowered. This will mean there are fewer so-called “ghost notifications”, according to the government.

NHS Test and Trace director of product, Gaby Appleton, said: “The team behind the app are continually working to improve its accuracy and user experience, to make it as simple as possible to keep users and their loved ones safe.  We are thrilled that over 19 million people have chosen to download the app to help protect their loved ones while preserving their privacy, and that over 680,000 QR codes have been created by businesses to support digital contact tracing. 

She added: “This update builds on that success by increasing accuracy, and also removing ‘ghost’ exposure notifications, meaning users will only be notified if they need to self-isolate. The more people who use the app, the better it works, so I encourage all those who have not yet downloaded the app to do so.”

The update was developed with the assistance of experts of the Alan Turing Institute – the UK’s national institute for data science and artificial intelligence. The government claimed the new functionality makes the NHS software “the only app globally” to have made such an update to the underlying Apple-Google infrastructure that is used by many countries around the world.

Mark Briers, programme director for The Alan Turing Institute's defence and security partnership, said: “It is thanks to the hard work of the NHS COVID-19 app development team and colleagues at the Turing Institute that we have been able to exploit the updated API technology in this way. This update increases the accuracy, meaning those most at risk will be notified to self-isolate.”

In addition to contact-tracing, the app also allows users to scan QR codes to check in to venues, enter test results, check symptoms, and read the latest government advice.

The government initially pursued a strategy of trying to build its own app based on centralised infrastructure, which would have allowed data to be gathered and analysed. However, after several months' work and more than £12m spent in supplier contracts alone, this project was abandoned after testing revealed that the technology worked only patchily on Android devices, and hardly at all on iPhones.

The app that finally made it to national release last month is instead built on a decentralised architecture jointly constructed by Apple and Google and used by the contact-tracing apps of many countries around the world. Using this model, no data is collected or stored anywhere other than on individual users' devices.

Sam Trendall is the editor of PublicTechnology, where a version of this story first appeared.

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