Thread trying to make sense out of why we still don't have the covid alert app in BC. Yesterday the PHO said that the app in the current form is not useful to augment contact tracing in BC, speaking about this starting at 39:35
The key point seems to be that the covid alert app is designed for maximal privacy, which comes with tradeoffs as to how much information people notified of an exposure and by extension PHO get. In particular the APP is designed so that users won't know when the exposure occurred
In practice this means the app is casting a wide net. Anyone that came into "close contact" with an infected person over the 14 days prior will get notified, even though the infected person likely wasn't infectious for the entire 14 day period.
The reason for this is that the app is designed so that health care workers can't link the exposure keys of the infected person to the infected person, so they can't filter the exposure keys to the likely infectious period.
Ontario deals with this by testing and reverse contact tracing everyone who received an exposure notification (and contacts public health), and then advises to either self-isolate (positive test), or self-isolate or self-monitor (negative test) depending on the risk assessment. 
That's not perfect, but seems like a good and useful protocol, taking the privacy level fixed. The BC PHO doesn't agree and wants a more invasive contact tracing app that allows the linking of infected individuals to their exposure keys so that they can be filtered.
The privacy tradeoffs are directly connected with people's willingness to use the app. Over 30% of Canadians have stated that they are unlikely to use a contact tracing app, and off those privacy was the main concern. doodles.mountainmath.ca/blog/2020/08/2…
As background, BCCDC has in the past pushed for a maximally invasive location tracking app, showing little appreciation for people's privacy concerns. This may explain why they are so averse to working with high user privacy app.
https://twitter.com/vb_jens/status/1260637672772472833?s=20
Anyway, to me this standoff appears to be driven by BC being uncomfortable with casting a wide net, and having less direct information, when contact tracing. The app could indeed be designed differently, e.g. in Germany people will know what day they have been exposed.
The question is not if the app should or should not expose more private information, it's if the app as it is now is a net plus for BC. I strongly believe it is. Could it be better? Maybe, but that can also be fixed after adopting the current app and is no reason to wait.
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