Contract tracing apps cannot replace face-to-face or telephone conversations, an expert has said.

The NHS Covid-19 symptoms tracking app was due to be rolled out in mid-May, following a trial on the Isle of Wight, as an aid towards the Government’s track and trace effort, but it is now expected in the “coming weeks”.

Currently NHS England’s test and trace system relies on contact tracers identifying people who have been in contact with a positive case of coronavirus and getting them to self-isolate.

Infectious disease specialist Professor David Heymann said that at present apps are not effective enough to be used alone.

He told a Chatham House briefing on Covid-19: “We do know though that you can’t replace that human element of contact with people who are sick, to identify their contacts, and then contact face to face with those contacts to make sure they understand what their responsibilities are.

“And also to identify contacts of them, should they become sick.

“So apps are going to be important to evaluate. I would volunteer to do it, but in the future they may have more of a role than they do now.

“Now they cannot replace the contact tracing, it’s face to face, or telephone to telephone.”

Dr Oliver Morgan is director of health emergency information and risk assessment in the Health Emergencies Programme at the World Health Organisation (WHO) Emergencies Programme.

He is in the middle of leading a three-day online global consultation on contact tracing.

He told the briefing: “I think some of the high level messages is that contact tracing when integrated into your Covid-19 response is really a critical element, both for managing risk and keeping that risk low.

“The other thing that we’re learning is that, yes, technology can help us to some degree.

“Really, we need the trained workforce, to be able to do effective contact tracing.

“And that has been reiterated from all the different countries and partners who are participating in this meeting.

“That’s even in places where they have tried to implement technologies to assist with contact tracing.

“It is the inquiry of trained contact tracer that yields the best contact tracing results.”

Dr Heymann also said that it is not too late in the outbreak to start contact tracing.

He added that like some European countries, the UK started with contact tracing, but did not continue with it.

He explained: “It happened because, in my analysis, and I think this is what most people believe, when it was noted how Italy was unable to accommodate all the patients who were becoming sick, and we’re seeing an increase in mortality.

“Countries began a reaction to follow what China had – just to lock down the economies in the hopes that they could flatten that curve of people who were infected.”