NHS Covid-19 app upgrade increases ‘accuracy’ in identifying close contacts


A screenshot of the NHS COVID-19 contact tracing app  (Photo by Gareth Copley/Getty Images)
A screenshot of the NHS COVID-19 contact tracing app (Photo by Gareth Copley/Getty Images)

THE NHS Covid-19 app has been upgraded to detect close contacts more accurately and users can now expect more high-risk notifications to be issued.



Due to the app’s improved accuracy, users who are notified to self-isolate should take warnings even more seriously, said a statement from the department of health and social care (DHSC).

The NHS Covid-19 app, which was built to anonymously track and warn people who are at risk of having been infected by the disease in England and Wales, relies on a Bluetooth-enabled API developed by Apple and Google for health services to develop decentralised, privacy-preserving contact-tracing tools.

Phones that are fitted with the app regularly generate random, anonymous IDs that are exchanged via Bluetooth whenever two devices that have downloaded the app come into prolonged contact.



If someone later tests positive for Covid-19, they have the option to submit their results to the app, which in turn triggers alerts to contacts deemed to be at risk of infection by the algorithm.

Gaby Appleton, NHS director of product for Test and Trace, has said that NHS Covid-19 app is the first in the world to integrate the latest upgrade in API by Google and Apple.

“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,” said Appleton.



“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 app uses a combination of distance, proximity and infectiousness of a contact to calculate the risk threshold at which someone is notified to self-isolate.

The app will be updated to better estimate distance between users to increase the accuracy of close contact notifications sent out by the app.



The improved algorithm was developed in collaboration with scientists from the Alan Turing Institute, and health services are now confident that the technology is highly accurate. The DHSC is, therefore, prepared to let the app issue more alerts to users than before, advising those who are at high risk of infection to self-isolate.

Mark Briers of The Alan Turing Institute 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.”

The app is also set to become interoperable with contact tracing apps in Scotland, Northern Ireland, Jersey and Gibraltar.

“We are currently consulting with the National Cyber Security Centre to ensure this process is secure and reliable, functioning effectively to benefit everyone using contact tracing apps across the UK. We expect this update to be released in early November,” the statement further said.