[Slartie]

His argument No. 1 is self-defeating. If you have rapid exponential growth and would have to publish hundreds of megabytes of keys per day (and phones only need to download the delta to the previous day), this approach of contact tracing is useless and you must instead get the entire population under lockdown. If everybody is sheltering at home, nobody needs notifications of possible contacts, because everybody is doing what would be the response to such a notification already. So you can simply disable the app in a certain country or don't accept submissions to the diagnosis server during that time.

This approach, just like the manual approach of tracking potential contacts via paper and phone, is only of use in a scenario with a very limited number of transmissions and an R (reproduction rate) of around or below 1. Its purpose is not to reach such a situation, but to aid in keeping that situation in effect without severe measures. But severe lockdowns must first suppress the infection counts to such levels before any contact tracing may work at all.

[cameronbrown]

I think the point with this is when the curve starts to flatten, we can _safely_ reopen the economy. Contract tracing and rapid response can end this.