Contact tracing apps are unlikely to be effective in reducing the spread of coronavirus unless there is a large-scale uptake by the population and it is supported by other public health control measures, scientists have said.

Their findings, published in the journal Lancet Digital Health, are based on a review of data from 15 scientific studies published between January and mid-April this year.

The researchers, led by University College London, also said evidence on the effectiveness of automated contact tracing systems is limited and there is an “urgent need for further evaluation of these apps”.

They added that even under optimistic assumptions, where up to 80% of smartphone owners across the UK are using a contact tracing app and more than 90% of the identified contacts are following quarantine advice, other public health control measures – such as physical distancing and closure of indoor spaces – would still be needed to keep Covid-19 infection under control.

Lead author Dr Isobel Braithwaite, of the UCL Institute of Health Informatics, said: “Across a number of modelling studies, we found a consistent picture that although automated contact tracing could support manual contact tracing, the systems will require large-scale uptake by the population and strict adherence to quarantine advice by contacts notified to have a significant impact on reducing transmission.”

She added: “Although automated contact tracing shows some promise in helping reduce transmission of Covid-19 within communities, our research highlighted the urgent need for further evaluation of these apps within public health practice, as none of the studies we found provided real-world evidence of their effectiveness, and to improve our understanding of how they could support manual contact tracing systems.”

We currently do not have good evidence about whether a notification from a smartphone app is as effective in breaking chains of transmission by giving advice to isolate due to contact with a case of Covid-19 when compared to advice provided by a public health contact tracer.

The researchers looked at more than 4,000 studies on automated and partially-automated contact tracing and found 15 relevant research papers.

But most of these studies were either based on modelling, or were observational or case studies, or did not include the full information needed to assess the effectiveness of contact tracing apps.

Dr Robert Aldridge, of UCL Institute of Health Informatics, said: “We currently do not have good evidence about whether a notification from a smartphone app is as effective in breaking chains of transmission by giving advice to isolate due to contact with a case of Covid-19 when compared to advice provided by a public health contact tracer.

“We urgently need to study this evidence gap and examine how automated approaches can be integrated with existing contact tracing and disease control strategies, and generate evidence on whether these new digital approaches are cost-effective and equitable.”

The researchers said that if implemented effectively, contact tracing apps may offer benefits such as reducing reliance on human contact tracers, but it could also increase the risk of Covid-19 among vulnerable groups and raises privacy concerns.

Dr Braithwaite said: “We should be mindful that automated approaches raise potential privacy and ethics concerns, and also rely on high smartphone ownership, so they may be of very limited value in some countries.

“Too much reliance on automated contact tracing apps may also increase the risk of Covid-19 for vulnerable and digitally-excluded groups such as older people and people experiencing homelessness.”