[fabian2k]

From looking at the specification, I don't see any serious loss of privacy there, if this is implemented as stated.

2) You don't need 100%, you only need enough to drop the R0 below 1. You'll likely need a majority of people using this, which is hard enough, but you don't need everyone using it.

3) The apps are not supposed to include every single registered contact, only contacts that are over a bit longer timeframe. A typical value I've heard is 15 minutes close contact, that is considered a high risk contact when contact tracing.

[vermilingua]

Minor nitpick: the R0 is the basic reproduction number, it describes the infectivity if no measures are taken to control the spread.

You’re looking for R, the effective reproduction number, which is R0 plus all controls.

[dbbk]

> 1. You'll likely need a majority of people using this, which is hard enough, but you don't need everyone using it.

It's going to be built into iOS and Android at the operating system level, and I assume have a very clear prompt to opt-in. It would not surprise me if it quickly reaches >50% of active users, at least for iOS.

Getting a timely Android update on the other hand...