Most of the countries using Apple and Google’s model do not alert people to self-isolate until a user has a positive test result.

The paper from Oxford also argued that the NHS version would lead to fewer people being told to self-isolate unnecessarily as the data collected would make it more accurate over time at working out which contacts were most likely to lead to infection.

Professor Christophe Fraser, of the BDI and an adviser to the NHS on the app, said: “These adjustments could potentially save more lives and build more trust and confidence for users that the system can effectively stop the spread of Covid-19.” 

A previous report by Oxford University last month found that an effective contact-tracing app could stop the spread of coronavirus before a vaccine is found if more than 56 percent of the population downloaded it and followed its advice.

That study said that any app would be far less effective if it waited until people had been tested to send self-isolate alerts because half of coronavirus infections happened before patients showed any symptoms.

However, Michael Veale, a lecturer at UCL who helped develop the Apple and Google system, said the NHS would still be able to send self-isolate alerts before a user had a test result if they switched over to the decentralised system.

He added: “There’s no technical reason why the Apple Google API couldn’t be triggered by a self-report.”

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