Lessons From Contact-Tracing and Exposure-Notification Apps
It’s been a year since the first contact-tracing and exposure-notification apps for the novel coronavirus appeared. The apps, which could inform people of exposure before they became infectious, had the potential to stem coronavirus spread. A 2020 Oxford University study estimated that if 56 percent of the population were using the app, this would be enough to suppress the disease’s spread (later variants of the virus appear to spread more easily, so a higher adoption rate would be needed in the face of the variants). So, how well have the apps worked in practice?
To make sense of that question, it’s worth examining how the apps work. They rely on Bluetooth signals to determine the distance between two app users’ smartphones. Singapore’s TraceTogether is one such app. TraceTogether was launched early and has achieved a usage rate of 70 percent. While use of TraceTogether is nominally voluntary, the use of the app is needed to enter any number of Singaporean establishments, including shopping malls, restaurants, offices and schools.
TraceTogether works like this: If Alyssa and Ben are in close proximity to one another and their phones are running TraceTogether, the devices will exchange identifiers that remain only on their phones so long as neither of them tests positive for the virus. But if Ben later tests positive Covid-19, the identifiers his phone has collected will be shared with Singapore’s Ministry of Public Health. The ministry will learn not only that Ben and Alyssa were in close proximity but for how long. TraceTogether is called a centralized app because the proximity information is processed centrally. Proximity information can be very revealing; it can show a person meeting with a friend who works for a competitor or that someone on parole is spending time with someone they shouldn’t be seeing. In Singapore, TraceTogether’s information can even be used in criminal investigations.
