How the NHS COVID-19 coronavirus contact tracing app works

The NHS COVID-19 smartphone app is now live.

Health Secretary Matt Hancock first revealed that the NHS was working on an app in April 2020. The app is 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 has being developed to replace it - which is now available to download.

Here's everything you need to know.

How does the NHS COVID-19 contact tracing app work?

The NHS COVID-19 app uses Bluetooth Low Energy (BLE) signals to keep track of phone handsets. It will detect when you're in significant contact with other individuals running the app via BLE, and using this method, build up a traceable contact map.

The app will use Apple and Google's contact tracing system, which is already in place on compatible Apple and Google devices. You'll need to be running iOS 13.5 or later (that's everything back to the iPhone 6S) or Android 6.0 or later (most phones from 2015 onwards) to be able to use the app.

If a user tests positive for COVID-19 it will trigger an alert to others they were in contact with who may need to self-isolate; equally, if you were in contact with someone who then later tests positive, you'll get an alert via the app, with all the advice about what you need to do.

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

The data will be anonymous and will remain on your phone unless you have to report something; you won't have to identify yourself via the app, so there's no way that others will be able to figure out who you are from the app or from the alerts they get. Everything will happen in the background, so once the app is setup, there is little else that you have to do.

How to install and setup the NHS COVID-19 app

Setting up the NHS COVID-19 app is easy.

1. Install the app from either the Apple App Store or from the Play Store for Android.
2. Open the app and follow the instructions.
3. You'll have to declare if you are over or under 16.
4. You will have to agree to a privacy notice, which says that data is stored on your phone for 14 days. The full privacy notice can be found here.
5. You will be asked to enter the first part of your postcode.
6. You'll be asked to turn on the Exposure Notifications system, click "turn on".
7. That's it.

Those are the only steps you have to take to get the app running on your phone. The postcode is used to give you a risk level for your area. Remember, your location isn't shared with other users or the government, all the information stays on your phone for 14 days, or until it is needed because there's a positive test result.

Now all you have to do is go about your business as normal, the app will run in the background on your phone.

What other features will the NHS COVID-19 app offer?

The app isn't just about contact tracing - or it's not only about the Bluetooth proximity logging. There are a range of other features to help us tackle the new age of living in a world with coronavirus.

The app will allow the scanning of QR codes at the entrance to buildings to further help establish contact networks should there be an outbreak. Currently many venues like bars and restaurants are asking customers to log their details to allow contact tracing if there's an outbreak linked to that location. Again, if you've been in a restaurant (for example) linked to an outbreak, but didn't come into close contact with the infected person (which wouldn't have been detected by a Bluetooth connection), then it allows another method to trace and alert you.

The NHS is encouraging venues to create QR codes to be scanned using your phone, so you'll get used to seeing those.

There will also be a symptom checker, so you can put in symptoms you're experiencing and the app will advise if you should get tested. The app will provide access to the NHS website for booking tests. You can also enter your test result code into the app if you test positive - this is what triggers the alert system to other users.

Finally, there's an isolation timer. If you test positive, or are experiencing symptoms, this will give you a countdown as to how long you should be in isolation, with a change on the screen telling you how many days you have left.

Following successful trials with residents on the Isle of Wight and the London Borough of Newham, and with @NHSVolResponder, the #NHSCOVID19app will be available nationally across England and Wales on Thursday 24 September.

Find out more: https://t.co/rzgGGmuV13 pic.twitter.com/PDXpJFkVwe

— NHS COVID-19 app (@NHSCOVID19app) September 11, 2020

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 BLE. 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 as soon as it is developed and ready for use.

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.

On 13 August the new app was launched into trials, with Dido Harding, executive chair of the NHS Test and Trace Programme, saying: "It's really important that we make it as easy as possible for everyone to engage with NHS Test and Trace. By launching an app that supports our integrated, localised approach to NHS Test and Trace, anyone with a smartphone will be able to find out if they are at risk of having caught the virus, quickly and easily order a test, and access the right guidance and advice."

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 point to an outbreak 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.

Adding QR code scanning is potentially a workaround, allowing centralised tracking of who goes where, outside of the system controlled by Apple and Google - although the specifics of how this part of the system works remains to be seen.

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

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 - did not include the over-70s in that group, because it was assumed they would be shielding at home when lockdown restrictions started to lift.

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

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