Learning from the initial deployment of digital contact tracing apps

International audienceLearning from the initial deployment of digital contact tracing apps Smartphone applications for digital contact tracing were a truly innovative intervention in the COVID-19 pandemic. These apps aim to automatically identify and rapidly notify individuals who have been in close contact with people who have tested positive for SARS-CoV-2. These apps were deployed in many countries in record time to support or complement traditional contact tracing systems. Epidemiological models showed the potential impact of this intervention under specific epidemic conditions, 1-3 but months into the apps' deployment, real-world evaluations are now required to identify shortcomings and look for improvements. In The Lancet Public Health, Florian Vogt and colleagues 4 report the findings from a prospective study of the deployment of COVIDSafe, Australia's national COVID-19 tracing app, in the state of New South Wales (NSW). The app was based on a centralised approach, in which the information of contacts is uploaded to a common database and accessed by public health authorities for risk assessment and notification. Analysing data from the first months of app deployment between May and November, 2020, the authors report that the app was used by 137 cases-ie, 22% of all 619 detected adult cases. Altogether, 205 contacts were recorded, among whom 79 (39%) qualified as clos