Contact tracing graphic

A contact-tracing app could help stop the coronavirus pandemic, but 80% of current smartphone owners would need to 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.

If there is lower uptake, academics say the app would still help slow the spread of Covid-19.

They add that letting people self-diagnose the illness could be critical.

That means users would only have to answer an on-screen questionnaire before being judged to be at significant risk of infection. They would not have to speak to a health advisor or wait for a medical test result.

This would send a cascade of alerts to people they had recently been in proximity to, advising