But evidence that these ‘contact-tracing’ apps work has been hard to come by, because most collect limited data to protect users’ privacy. Now, studies from a handful of nations show mounting evidence that apps can help prevent infections and are a valuable public-health tool.
Since the beginning of the COVID-19 pandemic, dozens of countries have deployed digital apps that attempt to identify people exposed to the SARS-CoV-2 coronavirus and stop onward transmission.
Researchers say that contact-tracing apps won’t by themselves bring the pandemic under control. But the results show they are useful, providing that they have adequate political backing and are properly integrated into public-health systems.
“These data are really appreciated, especially when it comes to decision-making — should we adopt the app or not?” says epidemiologist Viktor von Wyl at the University of Zurich, who has been evaluating Switzerland’s SwissCovid app.
Users are notified if someone they have come in contact with tests positive. The exposed user can then get tested or quarantine, which should help to prevent onward transmission.
Contact-tracing apps are installed on smartphones, and many involve the Google/Apple Exposure Notification (GAEN) system, which uses the phone’s Bluetooth signal to detect when two app users are close to each other — typically, within 2 metres of one another for more than 15 minutes.
The GAEN system prevents health authorities from gathering personal information about app users or their devices, thereby helping to address privacy concerns raised early in the pandemic. (This is not the case for all contact-tracing apps. Singapore’s TraceTogether app has attracted criticism because the data that it collects could be used by police in criminal investigations.)
On 9 February, researchers in Britain released an evaluation1 of the National Health Service (NHS) COVID-19 app, which was launched in England and Wales late last September. The evaluation, which has not yet been peer reviewed, found that the app sent out 4.4 exposure notifications for every user who tested positive for SARS-CoV-2 and agreed to the app notifying their contacts. That was more than twice the average of 1.8 contacts notified through manual contact tracing.