15 May 2020 – Policy Brief

Digital Proximity Tracing

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Proximity tracing (PT) is a novel method to support contact tracing. First mentioned in a previous policy brief on contact tracing, the method has met with considerable interest from the scientific community, policy makers, and the public. This document describes PT in more detail, specifically with respect to the PT app planned in Switzerland.

Executive summary

Contact Tracing is widely regarded as a crucially important method to bring the COVID-19 pandemic under control. Starting from a positive index case, contact tracing allows for the retrospective identification of contacts relevant for the transmission of SARS-CoV-2, which can then undergo precautionary isolation (quarantine). Rapid contact tracing is of particular importance in the COVID-19 pandemic due to the substantial contribution of pre-symptomatic transmission. Fundamentally, the strategy of contact-tracing and quarantining rests on the notion that quarantining can be applied very precisely, namely to the contacts of known cases, and thus in a limited fashion, instead of indiscriminately, which is the case during a lockdown where the vast majority of the population has to go into quarantine.

Contact tracing (CT) is classically done by trained personnel, thus requiring expertise and resources. At the beginning of the COVID-19 outbreak in Switzerland, person-based contact tracing capacities were quickly overwhelmed almost everywhere. The Swiss lockdown managed to rapidly decrease the daily reported case numbers, and cantons have since been asked by the Federal Office of Public Health to increase their person-based contact tracing capacities in order to deal with new cases during the post-lockdown period.

In the past few months, work has also started on so-called digital proximity tracing. Digital proximity tracing (PT) is the idea to use bluetooth-enabled smartphones (and potentially other bluetooth-enabled devices) to support person-based contact tracing. As mentioned in the policy brief on contact tracing and quarantine (Swiss National COVID-19 Science Taks Force, 2020), “digital proximity tracing uses very different methods from those of person-based classic contact tracing, with different implications for data privacy. Its ultimate goal is to rapidly notify users of possible exposure to an infected person whom they may not know personally. Person-based contact tracing and digital proximity tracing are complementary methods that work together to improve the effectiveness of a contact tracing strategy that contributes to SARS-CoV-2 prevention and control.”

In this document, we outline the basic functionality of the digital proximity tracing app to be deployed in Switzerland (in here referred to as the Swiss PT App, or PT app, as a final name has not yet been officially announced), and address common questions and concerns. As the PT app development is ongoing, the writing reflects the situation on the publication of this policy brief.

Date of publication: 15/05/202

In response to request from:

Comment on planned updates:

Expert groups and individuals involved: Digital Epidemiology & Contact Tracing

Contact persons: Marcel Salathé, Viktor von Wyl, Effy Vayena, Edouard Bugnon