Contract tracing app only effective if mass take up

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A contact-tracing app could help stop the coronavirus pandemic, but only if 80% of current smartphone owners use it, say experts advising the NHS.

The University of Oxford’s Big Data Institute has modelled a city of one million people to simulate the software’s impact. The team estimates that 56% of the general population must use the app to halt the outbreak, equating to 80% of all existing smartphone owners, based on data from Ofcom.

They add that letting people self-diagnose the illness could be vitally important, similar to the current Covid symptom tracker app. It means users would only have to answer an on-screen questionnaire before being judged to be at significant risk of infection, rather than them having to speak to a health advisor or wait for a medical test result.

According to the experts “speed is of the essence”. Even delaying contact tracing by even a day from the onset of symptoms could make the difference between epidemic control and resurgence. 

The Oxford University academics, a mix of epidemiologists and ethicists advising NHSX – the health service’s digital innovation unit –  first published a paper about its work at the end of March.

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However, the Contact Tracing app isn’t without problems. NHSX is believed to have changed plans from using a system that relied on GPS location readings and scanning QR codes to one that depends on Bluetooth.

This has been done to provide users more privacy and possibly encourage greater take-up. But a small number of phones still in use in the UK do not support the Bluetooth Low Energy system required, making the targets even harder to reach.

The app will use Bluetooth to determine who an infected individual was in contact with and notify their contacts to stay in quarantine. It’s hoped by using the app, as well as other measures such as hand-washing and social distancing from vulnerable members of the population, the UK can prevent a second peak in infections or the need for repeated national lockdowns.

On 20 March, Singapore became one of the first countries to deploy a voluntary contact-tracing app, TraceTogether. However, only about 12% of the population have installed it, and after a spike in new cases, the city-state introduced a lockdown on 7 April.

Chris Price
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