https://thenextweb.com/syndication/2020/10/24/why-contact-tracing-apps-havent-lived-up-to-expectations/

During the first wave of COVID-19, researchers at Oxford University built a computer model that suggested if 56% of the UK downloaded and used a contact-tracing app (alongside other control measures) it could end the epidemic in the country.

With the English app only available since September, it’s too early to tell how the system is actually doing. But even based on other countries whose apps have been available much longer, there’s still very little evidence that they can make a real difference to fighting COVID-19 – or that they can’t.