The news: British researchers calculated that its contact tracing app could have prevented 600,000 cases of covid-19. The announcement is good news for the system, which suffered serious starting problems—And a step forward for exposure notification systems more generally.
What they found: The study by a team of researchers from Oxford modeled the impact of 1.5 million notifications sent by the UK’s NHS app between October 1 and December 31, when nearly 2 million people were infected with covid-19. Their analysis showed that each person who tested positive and used their app to alert others sent an average of 4.4 notifications; without this intervention, they predicted there would have been between 200,000 and 900,000 more cases.
The data shows, as we previously reported, that even modest use of these apps can have a significant impact: “For every 1% increase in the number of users,” the researchers said, “we estimate the number of cases will decrease by 0.8% to 2.3% ”
This is good news for those who have tried to understand the effectiveness of these apps, which has been notoriously difficult to measure. Raphael Yahalom, a researcher at MIT’s Sloan School who has studied applications like these throughout the pandemic, says the article “represents the most comprehensive systematic analysis to date of a large-scale deployment. – and therefore, the most convincing proof of effectiveness. “
Why is this important: It is difficult to study whether contact tracing applications work because privacy concerns have made analysis particularly difficult, says Jenny Wanger, director of programs for the Linux Foundation Public Health. Many covid applications use the Google-Apple protocol, which is a system that keeps users anonymous. This protects user privacy so well that it is difficult for central health authorities or researchers to track information or see trends in alerts.
To get around this problem, the UK study looked at the number of notifications sent and compared it to what scientists knew about the behavior of the virus itself. Without knowing exactly who received the messages, the researchers were able to determine if the app was making a difference.
This approach will not work in each country with a covid application, although. Among other things, it requires some kind of centralized health system to track notifications. The United States, for example, does not have a national central database and instead uses a patchwork of state applications, although could change with the Biden administration.
Yet now that this technology is almost a year old, we might see more studies on how digital contact tracing works. Yahalom says there is more effort going, and a Swiss study was released earlier in February (although he cautions that it’s difficult to compare those studies directly).
Why we need to know: Exposure notification apps have had a hard time. In countries where they are voluntary, apps struggle to cope with low usage and privacy concerns. But knowing that they are effective may encourage some people to decide to download one and use one. More data could lead to more investment and more downloads, says Wanger, whose work supports the development and analysis of exposure notification applications. And more users means no more broken transmission chains.
This story is part of the Pandemic technology project, supported by the Rockefeller Foundation.