Performance of the Swiss digital contact tracing app over various SARS-CoV-2 pandemic waves: Repeated cross-sectional analyses.

BACKGROUND

Digital proximity tracing apps have been deployed in multiple countries to assist with SARS-CoV-2 pandemic mitigation efforts. However, it is unclear how their performance and effectiveness were affected by changing pandemic contexts and new viral variants of concern.

OBJECTIVE

The aim of this study is to bridge these knowledge gaps through a country-wide digital proximity tracing app effectiveness assessment as guided by the WHO/ECDC framework. Specifically, we performed a descriptive analysis of the digital proximity tracing app in Switzerland for three different time periods where different SARS-CoV-2 variants of concern (i.e., Alpha, Delta, and Omicron, respectively) were most prevalent.

METHODS

In our study, we refer to the indicator framework for the evaluation of public health effectiveness of digital proximity tracing apps of the World Health Organization / European Center for Disease Control (WHO/ECDC). We applied this framework to compare performance and effectiveness indicators of the SwissCovid app in Switzerland across three time periods that were characterized by the dominance of the Alpha, Delta, and Omicron variants of concern.

RESULTS

Average daily registered SARS-CoV-2 case rates during our assessment period from January 25, 2021 to March 19, 2022 were 20 (Alpha), 54 (Delta), and 350 (Omicron) per 100'000 inhabitants. The percentages of overall entered authentication codes from positive tests in the SwissCovid app were 10%, 4%, and 5% during the Alpha, Delta, and Omicron variant phases, respectively. Following receipt of an exposure notification from the SwissCovid app, 58% (Alpha), 44% (Delta), and 73% (Omicron) of app users sought testing or performed self-tests. Test positivity among these exposure-notified individuals was 19% in the Alpha (compared with 6% in the general population), 29% (11%) in the Delta, and 41% (43%) in the Omicron variant phases. In addition, 34% (Alpha), 19% (Delta), and 30% (Omicron) of exposure-notified app users reported receiving mandatory quarantine orders by manual contact tracing or through a recommendation by a health care professional.

CONCLUSIONS

In constantly evolving pandemic contexts, the effectiveness of digital proximity tracing apps in contributing to mitigating pandemic spread should be reviewed regularly and adapted based on changing requirements. The WHO/ECDC framework allowed us to assess relevant domains of digital proximity tracing in a holistic and systematic approach. While the Swisscovid app mostly worked as expected, our analysis revealed room for optimizations and further performance improvements. Future implementation of digital proximity tracing apps should place more emphasis on the social, psychological and organizational aspects to reduce bottlenecks and facilitate their use in pandemic situations.

CLINICALTRIAL