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iPhone issues see UK government dump centralised model for Covid-19 contact-tracing app

Department for Health makes U-turn on contact-tracing app after trial finds distances are not measured well enough, with particular detection problems for app users with Apple iPhones

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In the latest twist of the ongoing saga of its production, and hours after a government minister hinted that the much-delayed product may only be ready by winter, the development of the UK coronavirus contact-tracing app is to undergo a fundamental shift away from its much-criticised centralised model.

Health secretary Matt Hancock announced that the government is to abandon the development of the original version of the app after conceding that trials on the Isle of Wight found that it does not estimate distance well enough. He said that while the app had performed better on Android devices, there were significant detection problems for users with Apple iPhones.

Details of the current UK contract-tracing app were first revealed in April 2020, showing that it was to use a centralised model rather than the decentralised approach based on the Apple and Google application programming interface (API) used by contact-tracing apps launched in other countries.

The UK government originally chose to use Bluetooth Low Energy technology to automate what it called the “laborious” process of contact tracing, with the goal of reducing transmission of the virus by alerting people who may have been exposed so they can take appropriate action.

Once installed, the existing app uses Bluetooth to log the distance between a user’s smartphone and other nearby phones running the app. Under the centralised model, the anonymous log of user proximity is stored securely on each user’s phone. If a user becomes unwell with symptoms of Covid-19, they can use the app to inform the NHS, which, subject to sophisticated risk analysis, triggers an anonymous alert to those app users with whom the infected user came into significant contact over the previous few days. Distance is calculated as a function of the strength of the Bluetooth signal transmitted by other devices.

App accuracy and privacy criticised

Yet almost as soon as it was unveiled, the app attracted criticism over its technical foundations. The main thrust was twofold: Bluetooth technology was not robust enough for accurate measurement; and the centralised model would lead to data privacy issues, unlike the decentralised version using the Google and Apple API announced almost at the same time as the UK app. The latter technology is at the heart of the German government’s contact-tracing app which launched on 15 June. This product, too, started life with a centralised database, until German government scientists decided that using the Google and Apple API would see the product launched sooner.

The criticisms led to worries that the UK app would not be installed by enough people to make its availability meaningful in the fight against Covid-19.

Undeterred, the original version of the UK app and the timeline of development has always been staunchly defended by its authors, especially Matthew Gould, chief executive of NHSX, the UK health service’s digital innovation unit, which has been in charge of development.

On 4 May 2020, responding to the first wave of criticism along with a number of the UK’s most pre-eminent scientists who have been at the forefront of the UK’s response to coronavirus, Gould accepted that the app was no “silver bullet” and would only be effective as part of an overall telephone-based contact-tracing regime – which was subsequently launched on 27 May.

Gould said the centralised approach was taken so that NHSX could more easily optimise the algorithms it was using to perform analysis such as infection mapping for health authorities. “The model that we’ve taken allows us to see the whole population [usage] so we can make sure the risk model we’re using is as accurate as possible,” he said.

“There are a range of reasons why we’ve gone for the model we have, but it’s also worth saying another thing, which is there’s been a lot of talk about us and Apple and Google taking different approaches, but I did just want to say this: firstly, we’re working very closely with Apple and Google – this is not a competition. There is a huge amount of cooperation going on. And, as it develops, if we think there is a better way of doing what we need to do, we won’t hesitate to change.”

App development changes tack

And now it would seem that the better way has emerged. In a statement, the UK government said it had entered “the next phase” of development for the app to support the end-to-end NHS Test and Trace service by using the Google and Apple framework.

However, Hancock revealed that the trial programme hit substantial problems. It has been widely reported that the app detected contacts on only 4% of iPhones and 75% of Android devices. Hancock said the app in its current form did not estimate distance well enough, which is critical to any contact-tracing programme. He cited in particular iPhone-based apps, due to the fundamental nature of Apple technology – aspects of the iPhone operating system and power drain issues have previously been highlighted.

“What matters is what works, because what works will save lives. I will work with anyone – public or private sector, here or overseas – to gain any inch of ground against this disease. So, we’ve agreed to join forces with Google and Apple to bring the best bits of both systems together”
Matt Hancock, secretary of state for Health and Social Care

“As it stands, our app won’t work because Apple won’t change [its] system, but [while] it can measure distance, the app can’t measure distance well enough to a standard that we are satisfied with,” added Hancock. “For me, what matters is what works, because what works will save lives. And I will work with anyone – public or private sector, here or overseas – to gain any inch of ground against this disease. So, we’ve agreed to join forces with Google and Apple to bring the best bits of both systems together. We’ll share our algorithm and the work we’ve done on distance calculation and combine that with their work to deliver a new solution.”

The Department for Health and Social Care noted that an app based on the Google and Apple API did not yet present a “viable solution”, but was most likely to address some of the specific limitations identified through field testing in the Isle of Wight. It added that the Google and Apple solution does not currently estimate distance in the way required.

The UK government said the same problems had been faced by many countries around the world, and in many cases those countries were only discovering the issues after whole population roll-out. It singled out Singapore, whose TraceTogether contact-tracing app was launched in March, as a prime example.

The government added that bringing together work on the original centralised app and the Google and Apple system was “an important step”. Yet the previous few weeks saw a wave of government ministers hint that changes to the app were likely and that the original development had slipped way before the earlier promised launch dates.

On 11 May, communities secretary Robert Jenrick revealed the app had been downloaded by more than 50,000 people in the Isle of Wight trial – a third of the island’s population – and confirmed reports, highlighted by Computer Weekly on 8 May, that a radical change in the nature of the app was a possibility. On 11 June, in an admission of how the app’s prominence in the track and trace project was diminishing, health minister Edward Argar repeated the description of the app by NHS Test and Trace programme leader Dido Harding as “the cherry on the cake for this programme”.

On 18 June, junior health minister Lord Bethell, when asked about the contact-tracing app at a select committee meeting, said the app was not a priority right now and that it may be launched sometime before winter.

Covid response requires international collaboration

In a statement commenting on development of the new app, Harding and Gould said: “Our ambition is to develop an app which will enable anyone with a smartphone to engage with every aspect of the NHS Test and Trace service. 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.

“This change in line with other European nations is welcome. But this late U-turn means it is likely the UK will be waiting even longer for an app to be in use, which could pose a greater risk if there is a second wave of the virus”
Catherine Stihler, Open Knowledge Foundation

“We will also draw on the invaluable insight from all of those who trialled the app on the Isle of Wight – and the brilliant teams who have worked on it to date – to build an app that can form part of the end-to-end NHS Test and Trace service and this insight will be integral to the next phase of development.”

While still voicing concerns about data privacy issues, Catherine Stihler, chief executive of the Open Knowledge Foundation, said that by switching its plans for a centralised coronavirus-tracing app to a model based on technology provided by Apple and Google, the UK government was opting for something more privacy centric after “losing sight of ethical responsibilities” in the rush to develop its tools.

“This change in line with other European nations is therefore welcome. But this late U-turn means it is likely the UK will be waiting even longer for an app to be in use, which could pose a greater risk if there is a second wave of the virus,” she added.

No official launch date has been given for the new hybrid app. 

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