These estimated that, in just three months, the app prevented 284,000 or 594,000 cases, respectively — despite only 28% of the population in those regions using it. The study also suggested that for every 1% increment in app usage, the number of cases could be reduced by 0.8% and 2.3%, respectively.

The most compelling evidence yet, however, comes from an analysis published earlier this year of the usage and impact of the NHS COVID-19 app in its first year of deployment10. It found that the app prevented around one million infections and saved more than 9,600 lives in England and Wales between September 2020 and September 2021. And it achieved this even though, on average over the year, only around 25% of the population was using it (see ‘What the data say’).

Honestly, I did think the contact exposure apps were a failure. I almost never got notifications, despite leaving them always on, and legitimately it sounds like adoption was low. But it sounds like they were still having a noticeable effect.