[mjlawson]

Immuni is the official contact tracing app for Italy with 10mm downloads.

[tgragnato]

Which is not "nobody", but it is not even close to the statistical threshold of "enough use, helps prevent the spread of the disease"

[SahAssar]

Globally yes, but the thing about contact tracing is that it is inherently local. So getting 1/6:th (if we assume most of those downloads are in Italy) of a single country would probably be helpful in preventing spread.

[DuskStar]

It means 1/36 interactions will be recorded by the app, which is almost certainly not enough to move the needle.