Coronavirus: Contact Tracing

(asked on 6th July 2021) - View Source

Question to the Department of Health and Social Care:

To ask Her Majesty's Government what assessment they have made of the accuracy of the NHS COVID-19 contact tracing app in identifying close contacts with people who test positive for the virus.


Answered by
Lord Bethell Portrait
Lord Bethell
This question was answered on 20th July 2021

The app uses Bluetooth Low Energy to understand the distance over time between people who have downloaded the app. If someone tests positive for COVID-19, the app’s risk-scoring algorithm uses this data, along with the infectiousness of the individual testing positive, to make calculations about the risk of transmission and who should receive an alert. If a notification to self-isolate is received, the user’s device has been in close proximity to the device of someone who has recently tested positive. For its ability to judge proximity, the app achieves ‘excellent’ performance by scientific standards.

Prior to the launch of the app it was tested in a range of environments, in order to evaluate its effectiveness at accurately measuring distance. The app has also been modelled in simulations involving hundreds of thousands of scenarios. The app performed as expected and we are confident that it can accurately detect distance in different settings. As Apple and Google develop aspects of the underlying contact tracing technology, they have also conducted their own tests related to accuracy.

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