How does Scotland's new contact-tracing app work?

BBC Technology 10 Sep 2020 06:07
Contact appImage copyright PA Media

Scotland now has its own proximity tracing app to help combat the spread of Covid-19. People with smartphones are being urged to download Protect Scotland as soon as possible to help boost the Test and Protect system.

How does it work?

The app uses Bluetooth technology to alert users if they have been in prolonged close contact with someone who has since tested positive for Covid-19.

When an individual tests positive for the virus they are contacted by a contact tracer via text, phone or email.

The contact tracer will ask them if they are an app user and if they are willing to use the app's upload function to anonymously alert close contacts.

If they agree, they'll be sent a unique code to their mobile which unlocks this function on the app.

By sharing their positive test result in this way it forms part of an anonymous database.

The app on other users' phones regularly checks this database to see if they have been in contact with an infected person.

Where can you get it?

Protect Scotland can be downloaded for free from Apple's App Store or Google Play.

Essentially, any phones released after 2015 should have the ability to run the app.

Yes. The app uses anonymous codes or "keys". These will be exchanged between phones via Bluetooth but they contain no personal data.

Using the app is entirely voluntary and you don't have to enter any personal details to download or install it.

Your phone will check them against the database to see if any of these keys were "infected" but it won't upload any information without your permission.

How does it tie in with Test and Protect?

Up until now contact tracing has been done manually using a method used for years to help control the spread of infectious diseases.

These close contacts are then phoned and given advice.

What about false positives?

Some users are advised to turn their phones off, or disable Bluetooth, in some circumstances. For example, these would include health or social care workers in clinical settings who are wearing medical grade PPE.

The developers say there is always a chance that false positives can be generated - such as through the wall of a house or flat - but the risk is "very low".

How many people need to download the app for it to be effective?

The Scottish government has pointed to an Oxford University study, which claims that even with an uptake of just 15%, a contact tracing app can drive down infections by about 8% and deaths by about 6% - if it is part of a manual track and trace strategy.

Is this based on the Irish system?

The app being adopted in Scotland is instead based on a system developed in Ireland by the software firm NearForm.

NearForm designed it using a toolkit made available to developers by Apple and Google

Image copyright NearForm

NearForm's system has also been adopted in Northern Ireland.

The Scottish government said it anticipated Protect Scotland would work with equivalent apps in the Republic of Ireland, Northern Ireland and Gibraltar by the end of September.

The app being developed by NHS England didn't initially use the Apple/Google toolkit, but that decision was reversed in June.

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