Background: Digital proximity tracing applications were rolled out early in the COVID-19 pandemic in many countries to complement conventional contact tracing. Empirical evidence about their benefits for pandemic response remains scarce. We evaluated the effectiveness and usefulness of 'COVIDSafe', Australia's national smartphone-based proximity tracing application for COVID-19.
Methods: In this prospective study, conducted in New South Wales, Australia between May and November 2020, we calculated the positive predictive value and sensitivity of COVIDSafe, its additional contact yield, and the number of averted public exposure events. Semi-structured interviews with public health staff were conducted to assess the application's usefulness.
Results: There were 619 confirmed COVID-19 cases and over 25,300 close contacts during the study period. COVIDSafe was used by 137 (22%) cases and detected 79 (0.3%) close contacts. It had a positive predictive value of 39% and a sensitivity of 15%, and detected 17 (0.07%) additional close contacts that were not identified by conventional contact tracing. The application generated a substantial additional workload for public health staff and was not considered useful.
Conclusions: COVIDSafe was not sufficiently effective to make a meaningful contribution to the COVID-19 response in Australia's most populous state over a 6-month period. This contrasts optimistic projections from modelling studies about the added value of digitally supported contact tracing. We found no evidence that it adds value to conventional contact tracing, and recommend that their implementation should always include comprehensive effectiveness evaluations.
Effectiveness of digital contact tracing for COVID-19 in New South Wales, Australia