26 August 2020


Potential reduction in transmission of COVID-19 by digital contact tracing


Executive Summary

  • To maintain elimination of COVID-19, digital contact tracing systems should be designed to complement manual contact tracing, for example by enhancing coverage or speed of tracing, rather than as a separate or fully automated system.
  • To reduce the effective reproduction number to around 1 requires a combination of rapid testing and case isolation, a well-functioning manual contact tracing system, digital contact tracing with an uptake rate of at least 75% and recording 90% of close contacts, and highly effective quarantine of traced contacts.
  • Ensuring that individuals with COVID-19 symptoms get tested quickly and are able to isolate effectively is just as important as investment in contact tracing.
  • Digital systems based on QR codes with no proximity detection are likely to be less effective as a result of recording fewer contacts.
  • Bluetooth apps and card-based proximity detection systems perform comparably at a given level of coverage, but other factors such as usability, reliability and longevity need to be considered.
  • In the event of a large ongoing outbreak, scalability and false positive rates are more important, but significant population-wide control measures are also likely be required to prevent a major epidemic.
  • Tracing and quarantining second-order contacts of a confirmed case provides a relatively small additional benefit. This could be useful in the very early stages of an outbreak, but for a larger outbreak ensuring fast and effective quarantine of first-order contacts should be a higher priority.