Contract tracing apps used to reduce the spread of COVID-19 are unlikely to be effective without proper uptake and support from concurrent control measures, according to a new study.

Researchers at University College London (UCL, United Kingdom) conducted a systematic review of studies that examined the use of automated or partly automated contact tracing of COVID-19, severe acute respiratory syndrome (SARS), Middle East respiratory syndrome (MERS), influenza, or Ebola virus spread. The primary outcomes were the number or proportion of subsequent contacts identified; secondary outcomes included indicators of outbreak control, uptake, resource use, cost-effectiveness, and lessons learnt. In all, 4,033 papers were reviewed, of which 15 were identified with useful data.

The results showed no empirical evidence of the effectiveness of automated contact tracing. Four of the seven studies suggested that to control COVID-19, high population uptake of automated contact-tracing apps (56-95%) is required, typically alongside other control measures. Partly automated contact tracing generally reported more complete contact identification and follow-up, compared with manual systems. The researchers concluded that at present, reliance on automated contact tracing approaches without additional extensive public health control measures is unreliable. The study was published on August 19, 2020, in Lancet Digital Health.

“Although automated contact tracing shows some promise in helping reduce transmission of COVID-19 within communities…none of the studies we found provided real-world evidence of their effectiveness,” said lead author Isobel Braithwaite, MBBS, PhD, of the UCL Institute of Health Informatics. “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.”

Contact tracing is a method used in the management of infectious disease outbreaks, which aims to interrupt chains of infection transmission through quarantine of contacts, and has formed part of the response to the COVID-19 pandemic in many countries. It involves a person recalling their recent close contacts and activities; those deemed to be at risk of infection are then contacted and advised to take action to reduce onward transmission by self-quarantine for a specified time period.

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