Efficacy of app-based Covid-19 contact tracing systems is limited, finds study

Contract tracing apps or manual contract tracing may not be able to contain the spread of the Covid-19 pandemic without effective public health control measures, including social distancing, according to the study published in the journal Lancet Digital Health. The study stated that the efficacy of automated contact tracing systems is very limited.

The authors noted in their findings that typically, the limitations of contact tracing include incomplete or incorrect recall of contact events by cases.

They also mentioned that the time taken to notify contacts manually can delay quarantine. The process is also resource-intensive and time-consuming.

The researchers analysed 4,033 records from database searches; two further relevant studies were identified through professional networks and one from reference lists of included studies.

Authors stated that manual contact tracing on a large scale is still likely to be required in most contexts, and there is a clear need for further research to strengthen the evidence base for automated contact tracing.

Factors that determine effectiveness

The effectiveness of contact tracing depends on the disease context; system factors, such as the timeliness of case identification and contact notification, contact tracers' expertise, and the case and contact definitions used.

It also depends on context-dependent social and behavioural factors such as self-reporting rates and quarantine adherence.

Lead author Isobel Braithwaite from UCL said in a statement: “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.”

“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,” Braithwaite added.

“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,” Braithwaite further noted.

Lack of evidence

The review shows that, at present, there is insufficient evidence to justify reliance on automated contact tracing approaches without additional extensive public health control measures. “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 the advice to isolate due to contact with a case of Covid-19 when compared to advice provided by a public health contact tracer,” said Robert Aldridge from UCL Institute of Health Informatics.

“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,” Aldridge said.