How the NHS COVID-19 coronavirus contact tracing app will work

The UK government is working on a  COVID-19 contact tracing app. Health Secretary Matt Hancock first revealed that the National Health Service's digital innovation branch, NHSX, was working on an app that will help track the spread of COVID-19 in April 2020. The app is simply called NHS COVID-19 and it's designed to work alongside the UK's Test and Trace scheme that started on 28 May 2020.

"If you become unwell with the symptoms of coronavirus, you can securely tell this new NHSX app, and the app will then send an alert anonymously to other app users that you've been in significant contact with over the past few days, even before you had symptoms so that they know and can act accordingly," explained Hancock during a UK daily pandemic briefing.

Since it's original announcement, the app has been trialed, scrapped and a second app is being developed to replace it. Here's everything you need to know.

How will the NHSX contact tracing app work?

The NHSX contact tracing app will use Bluetooth Low Energy (BLE) signals to keep track of handsets and relay that data. It will detect when you're in significant contact with other individuals running the app via Bluetooth, and using this method, build up a traceable contact map.

You won't share anything until you need to make a report, with all the data remaining on your phone until you need to report that you're having COVID-19 symptoms. Each user will have randomised ID numbers so it won't reveal who you are or who you came into contact with.

The mobile app will work by letting users self-report if they're experiencing symptoms of the virus and then via that anonymous contact map, send notifications to those significant contacts that the infected user has been in contact with. The app will use Apple and Google's contact tracing system, with the UK having faced technical challenges when developing its own app; it's now reportedly working with Germany to use some of its code to get the UK system off the ground.

The German ambassador Andreas Michaelis told BBC R4 that the German app works and has so far seen a 14 million installs in the country.

If a user tests positive for COVID-19 it will trigger an alert to others they were exposed to who may need to quarantine. For those who need testing, the app should provide a route into getting a test from the NHS, as well as get the latest UK advice on self-isolation.

Use of the app will go hand-in-hand with the HNS Test and Trace contact tracing system carried out by humans, as well as the wider testing network that's now available in the UK. 

What part do Google and Apple have to play?

Google and Apple announced on 10 April that they were jointly working on an API (application programming interface) that would allow Android and iPhone devices to anonymously share the data needed to carry out contact tracing, using Bluetooth Low Energy. As Apple and Google jointly control pretty much the entire smartphone market, this would cover virtually all smartphones in use, except some much older models, of which there are few in the UK.

The pieces needed for this system have been updated on most active iPhone and Android handsets, meaning they are ready to interface with the NHS app once it is developed.

This provides a platform that healthcare agencies can use to get the data from devices to share with other users. In the future, the system would allow Google and Apple devices to handle the data at a system level, decentralising that data and ensuring that privacy is protected by the terms of Apple and Google respectively. That means you won't have to have the app open and running all the time - it will work in the background and would also mean that the data remains private.

It was originally confirmed that the NHS wouldn't be using the Apple and Google system, however Matt Hancock, in response to questions from the BBC on 5 May 2020, confirmed that the NHS continued to work with Apple and Google. It emerged on 8 May that NHSX had commissioned a second app using the Apple-Google system according to The Financial Times, before final confirmation on 18 June that the UK would be shifting its app over to the Apple and Google system.

The Department of Health and Social Care was keen to stress that the Apple and Google parts of the system alone do not make for a complete app and that more work is needed, especially around estimating distance between app users. In this regard, the UK will be working in collaboration with Apple and Google to share its own learnings, although how much truth there is in this claim remains to be seen.

"Our response to this virus has and will continue to be as part of an international effort. That is why as part of a collaborative approach we have agreed to share our own innovative work on estimating distance between app users with Google and Apple, work that we hope will benefit others, while using their solution to address some of the specific technical challenges identified through our rigorous testing," said Baroness Dido Harding, executive chair of NHS Test and Trace and Matthew Gould, CEO NHSX in a joint statement. 

Talking in the Downing Street briefing on 18 June 2020, Matt Hancock, Health Secretary said that the Apple and Google system "does not measure distance well enough ... [and] our app won't work because Apple won't change its system," before going on to confirm that the NHSX distance measuring algorithm was to be shared with Apple-Google to help improve their systems.

Importantly, the Apple-Google system is decentralised, whereas the original proposed system had been centralised.

What is a centralised and what's a decentralised system?

A lot of the discussion around contact tracing apps talks about centralised and decentralised systems. In a centralised system, all the data heads into a central server for processing. This is the system that France, Australia and Norway, for example, are aiming to use. 

The advantage of a centralised system is that the authorities can use the data to get more information about how the virus is spreading, locations where there's a lot more contacts reported which might points to a outbreak hotspot that needs some other form of intervention.

A decentralised system only shares data between phones, meaning that it's a lot more private and secure, because that data can't be accessed by anyone else, like a government body. 

Originally NHSX had wanted to use a centralised system, saying: "It would be very useful, epidemiologically, if people were willing to offer us not just the anonymous proximity contacts but also the location of where those contacts took place - because that would allow us to know that certain places or certain sectors or whatever were a particular source of proximity contacts that subsequently became problematic," said CEO of NHSX Matthew Gould, according to TechCrunch, when the app was discussed at the Common's Science and Technology Committee on 28 April 2020.

As the app has now changed how it's going to work at its core, that's unlikely to be possible. 

How many people will need to use the NHS app to make it effective?

The NHSX thinks more than 60 per cent of the population needs to use the app for it to be effective in helping the country return to normality, but more recent reports have suggested that 80 per cent of smartphone users (56 per cent of the population) would have to use it for the best results, according to experts at the University of Oxford talking to the BBC.

The big data team at Oxford - advising the NHSX team - has not included the over-70s in that group, as it's assumed they will be shielding at home when lockdown restrictions start to lift, although there will be some benefits if the uptake is a little lower. In Singapore, where a similar system was tried, the uptake was only 12 per cent, although the launch of a similar system in Australia, called Covidsafe, saw over 2 million installs in a matter of days. 

The problem is getting high numbers of people to use any app, especially as it's going to be voluntary to use. 

When will the NHSX contact tracing app be available?

The NHSX contact tracing app is currently in development and is not yet available to download and use on iPhones and Android devices. 

The old version of the app was originally test on the Isle of Wight. Announced by Hancock at the Downing Street briefing on 4 May 2020, the Health Minister outlined that the Isle of Wight made a perfect testing ground for the system because it's isolated, has one authority and one NHS Trust, and fairly low levels of coronavirus currently. That trial has finished and the app has been discontinued while a new solution is developed.

The UK Government initially said they were looking at the middle of May for a launch, but that date has now come and gone. The middle of June was suggested, followed by a statement confirming the switch to the Apple-Google system instead on 18 June, with the timeline looking more like the end of the year.

The Department of Health and Social Care says the NHS app "...does not yet present a viable solution, at this stage an app based on the Google/Apple API appears most likely to address some of the specific limitations identified through our field testing. However, there is still more work to do on the Google/Apple solution which does not currently estimate distance in the way required." 

Talking on 18 June at the Downing Street briefing, Hancock said "we're working on it," when asked when the app would be available, before going on to stress that they wouldn't launch the app until they were sure that it would do the job required.

What about the EU's rules?

The EU has outlined how it believes that contact tracing apps should work for EU member states - and that's going to include scrutiny of Apple and Google's system, to ensure that it dovetails with the EU's own privacy rulings. Those things include that an individual shouldn't be able to be identified through the system and that it is disabled once the need for contact tracing has passed.

The EU has essentially mandated that either a centralised system or a decentralised system will be accepted, as long as it's only used for coronavirus contact tracing, anonymised and voluntary.  

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