An update that intended to alert users spending only a few minutes in proximity to a highly infectious person never took effect

Credit: unreguser/Xinhua News Agency/PA Images

A flaw in the NHS Covid-19 contact-tracing app saw people only advised to self-isolate if they had spent five times as long potentially exposed to coronavirus as the time period at which a notification was intended to have been triggered, it has been reported.

According to a story in the Guardian, an update made shortly before the national launch of the app in September intended to incorporate a consideration of infectiousness. Part of the intent of this change was that people would be alerted to isolate after just three minutes within two metres’ proximity to someone likely to be at the peak of infectiousness – which is immediately after they begin displaying symptoms.

This is five times as quick as the previous threshold of 15 minutes across the board with which the app was developed and tested.

But, according to the newspaper, this planned alteration did not take effect and, as a result, users of the contact-tracing app were only notified to isolate after 15 minutes in close contact with a highly infectious person and almost 40 minutes near someone yet to display symptoms but still potentially infectious.

The Sunday Times quoted a government source as claiming that, because of the programming error, a “shockingly low” number of people had been notified to isolate in the six weeks since the app first launched.

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The flaw was reportedly only detected last week during the process of rolling out another update, which is intended to improve the app’s ability to use Bluetooth to calculate distance, and to end the issuance of so-called ‘ghost notifications’ – in which users are warned they may be at risk, but not subsequently told to isolate.

A Department for Health and Social Care spokesperson told the Guardian that, following the latest update: “We anticipate more app users who are at high risk of having caught the virus will receive a notification to self-isolate, and that will be to everyone’s long term benefit by reducing the chances of those with the virus passing it on to others. We are very clear, everyone who is contacted will have been in close contact with someone who has a confirmed case of Covid-19.”

Since development started back in March, the app has been just one troubled strand of a Test and Trace programme that has repeatedly fallen short of expectations.

Like a number of other countries, the UK began by trying to develop its own centralised technology – which would allow for data gathered by the program to be collected in one place and analysed by public-health officials. Development of the technology – on which the government had already spent more than £12m in supplier contracts alone – was scrapped in June, once it was discovered that the software worked only patchily on Android devices, and barely at all on iPhones.

At this point the government then began work on adapting the decentralised architecture jointly created by Apple and Google. Using this system, no data is stored anywhere other than on users’ devices.

The government finally launched a contact-tracing app across England and Wales on 24 September, six months after beginning work and three months after scrapping plans for its own centralised app.

By contrast, a number of other countries that tried to build their own centralised technology – including Germany and Denmark – had, by the time the UK gave up on the process, already changed course and successfully developed and launched national apps based on the Apple-Google system.