Among other things, to be most effective there has to be two-way information flow with public health authorities who do contact tracing. When somebody is found

Among other things, to be most effective there has to be two-way information flow with public health authorities who do contact tracing. When somebody is found to be positive, that info needs to propagate into the app and through the likely-spread network. I believe that simply cannot be done by private entities under the framework of existing health privacy regulation. Similarly, when the tracking system identifies someone as high risk, they need to be referred to testing by public health at the least. It also makes sense that a high risk person be isolated or quarantined, and it's possible the benefits of enforcing that through police outweigh the risks. If so, that's clearly a government function, not something that can be done by Google.