NHSX, the digital transformation arm of the UK’s NHS (National Health Service) is working on an app that will traces close contacts of people carrying the COVID-19 virus and advise them to self-isolate, the Guardian reports. The app is reported to be in advanced stages of evaluation, and weeks away from being ready to be deployed.

The report says that for the app to be effective, around 60 per cent of the adult population would need to sign up and engage with the app by registering their symptoms or positive test results. Their proximity to other users would be logged, and they would be given advice, via alerts, to self-isolate, even if not aware of having been in contact with someone infected.

The app would not need to access location data, but could log users’ proximity to each other via Bluetooth. Once a user reports symptoms or a positive test result, the app would trace back through close contacts over the past seven days and alert those calculated to be at risk. Once deployed, developers would use data on who is actually infected to optimise the app’s performance and gain further insights into how transmission occurs.

While the idea of such an app has raised concerns over privacy and surveillance, the report notes that digital contact tracing has been a central part of the containment strategy in China, and also references new analysis by scientists at Oxford University that says that “digital herd protection” is likely to be crucial in order to lift current restrictions, without seeing a huge resurgence of infections.

“We see it as the only alternative to … applying isolation to the whole population,” Professor David Bonsall, senior researcher at Oxford University’s Nuffield Department of Medicine and a clinician, who co-led the project, told the Guardian. “We think it’s going to be a very important part of that strategy.

“That’s where this concept of herd protection came from. You can protect the vulnerable people in society who may not have smartphones, and protect children. If enough adults across the population engage with the system and trust the system telling them they should isolate, you’re protecting all those individuals who don’t have a device.”

A high proportion of transmission of COVID-19 occurs before a person is showing symptoms, so isolating people once they become ill and tracing contacts manually has limited effectiveness because the spread of the virus will be one step ahead, according to the Oxford University team’s analysis in the journal Science.

The team has been working on an algorithm for the app since mid-January and has studied the Chinese app that gives people a red or green code determining whether they need to self-isolate.