This article discusses how to exchange COVID-19 contact tracing information between countries that use contact tracing apps and infrastructure. It takes a structured look at the goals, challenges, opportunities, and limitations of this kind of interoperability between national systems. This article is not intended as an introduction to contact tracing, nor as an opinion piece if and how app-based contact tracing is an effective way to improve national and international management of the Corona virus pandemic.
Contact tracing is an epidemiological method for understanding and tracking the spread pattern of infectious diseases. It works by tracing back the contacts that an individual had who at some point is diagnosed as being infected. The goal is to find contact persons in that individual’s recent past so that they can be quarantined and tested. App-based contact tracing is a way how to complement traditional ways of contact tracing by using mobile phones and their sensors to create traces and thereby tracking past contacts.
In general, mobile phones trace an individual by location, by their proximity to others, or by a combination of these methods. This information is collected by and stored on the phone, and then all or some of this information then is sent to a server. The “What is Contact Tracing? And how do the apps work?” video provides an overview of the various elements of this picture, and how communications between them work.
Decentralized vs. Centralized Approaches
A major discussion recently has been how to handle the data that is being collected. There are two general approaches, and both of them are favored by several countries for designing and building their national systems:
- The centralized approach forwards the data of all individuals to a central server, where it is stored and can be analyzed. The advantage of this approach is that countries have a comprehensive dataset for their analysis. The disadvantage is the loss of privacy, which in itself is an important good to contemplate, and also may play heavily into the willingness of the public to use the contact tracing app.
- The decentralized approach keeps data on the phone and only transmits data to the server when an individual is diagnosed as being infected. In that case, the history of that individual is transmitted to a server, which then distributes it to all other users’ phones. The check for contact (and thus possible exposure to the virus) then is done locally on all phones. The advantage of this approach is that it preserves privacy, and thus may see better acceptance by users. The disadvantage is that countries do not have access to the full data (except for the anonymized identifiers of diagnosed individuals), and therefore cannot use it for analysis.