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Germany's Covid contact tracing app is Open Source

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Re: Germany's Covid contact tracing app is Open Source

#21

Post by celticninja »

Someone wrote: post #17
fabian2k wrote: post #12

Earlier quoted context omitted.

The biggest risk are longer contacts, not very short ones. You don't want to notify everyone that passed that person on the street, but you do want to notify everyone that was reasonably close in the same train for half an hour. This is pretty much just an extension to classic contact tracing. And there you also have to work with very rough categories of risk, this isn't so much different.

I don’t see why N S-second contacts would be lower risk than one N×S-second one. This isn’t a matter of ‘small doses can’t harm you’, is it?

Viral load does seem to play a part in severity of the response by the immune system

Re: Germany's Covid contact tracing app is Open Source

#22

Post by DiogenesKynikos »

mikece wrote: post #13

I wonder how quickly contact tracing applications will be leveraged for other uses. If a significant number of protesters are using such an application then I imagine government will throw the “for your protection“ excuse to go harvest information from the phones of protesters to see who was meeting with him and who their social circles are. Of course, to keep us and our children safe.

That's a legitimate concern, but I think the German app is designed so that the government does not get the contact data.

Here's how I understand the system:

Your phone saves the ID numbers of the phones it's come into close contact with. The IDs are randomly generated, so they don't contain any information about the person carrying the phone. When someone tests positive for the virus, they can transmit their ID to a central server, which then broadcasts that ID to everyone with the app. The app checks that ID against its local list of contacts.

Re: Germany's Covid contact tracing app is Open Source

#23

Post by CaptainZapp »

Someone wrote: post #17
fabian2k wrote: post #12

Earlier quoted context omitted.

The biggest risk are longer contacts, not very short ones. You don't want to notify everyone that passed that person on the street, but you do want to notify everyone that was reasonably close in the same train for half an hour. This is pretty much just an extension to classic contact tracing. And there you also have to work with very rough categories of risk, this isn't so much different.

I don’t see why N S-second contacts would be lower risk than one N×S-second one. This isn’t a matter of ‘small doses can’t harm you’, is it?

Actually it makes a huge difference.

You need to absorb a certain amount of payload in oder to get infected.

I found this article[1] on the subject extremely enlightening.

[1] https://www.erinbromage.com/post/the-risks-know-them-avoid-t...

Re: Germany's Covid contact tracing app is Open Source

#24

Post by [deleted] »

Someone wrote: post #17
fabian2k wrote: post #12

Earlier quoted context omitted.

The biggest risk are longer contacts, not very short ones. You don't want to notify everyone that passed that person on the street, but you do want to notify everyone that was reasonably close in the same train for half an hour. This is pretty much just an extension to classic contact tracing. And there you also have to work with very rough categories of risk, this isn't so much different.

I don’t see why N S-second contacts would be lower risk than one N×S-second one. This isn’t a matter of ‘small doses can’t harm you’, is it?

[deleted]

Re: Germany's Covid contact tracing app is Open Source

#27

Post by w-m »

Schlaefer wrote: post #18
uvw wrote: post #11

Earlier quoted context omitted.

I imagine it's not meant to be 100% accurate. If it identifies even 50% of the people that may have come in contact with someone who's positive, even considering 50% false positives, I would consider it a rousing success.

Even if there are 95% false positive: if you're able to test all those people and catch the 5% that might still be a net profit. It comes down to cost. Societies are spending thousands of billions to mitigate the problem, even a slight reduction of that number is a win.

As far as I understand, you would need to send everybody who might have been in contact with someone who's positive into quarantine, right away. You can also test them, but you need to quarantine them immediately, as the virus is transmitted before symptoms show.

If you just send everybody who was in contact with a positively tested person into testing (they give samples, send them in, get tested, get the results back), but they keep going about their normal lives, they will statistically infect more people before the tests come back.

So the false positive rate is quite important, as it potentially means sending thousands of people into home-quarantine.

Re: Germany's Covid contact tracing app is Open Source

#29

Post by Schlaefer »

w-m wrote: post #27
Schlaefer wrote: post #18

Earlier quoted context omitted.

Even if there are 95% false positive: if you're able to test all those people and catch the 5% that might still be a net profit. It comes down to cost. Societies are spending thousands of billions to mitigate the problem, even a slight reduction of that number is a win.

As far as I understand, you would need to send everybody who might have been in contact with someone who's positive into quarantine, right away. You can also test them, but you need to quarantine them immediately, as the virus is transmitted before symptoms show. If you just send everybody who was in contact with a positively tested person into testing (they give samples, send them in, get tested, get the results bac…

> So the false positive rate is quite important, as it potentially means sending thousands of people into home-quarantine.

Of course it's important and of the course the lower the false positive rate the better. But the argument remains: even with a high false positive rate, what's the net result? Maybe overall it's worth putting thousands of false positive in quarantine now than a whole city of millions two months later.

There are so many variables and known unknowns in this approach. I argue that even with all the well reasoned arguments against, at this scale and with this stakes they stay theoretical until we actually do it. Let's try at least once, and if it fails it's still knowledge gained.

Re: Germany's Covid contact tracing app is Open Source

#30

Post by tzs »

CaptainZapp wrote: post #23
Someone wrote: post #17

Earlier quoted context omitted.

I don’t see why N S-second contacts would be lower risk than one N×S-second one. This isn’t a matter of ‘small doses can’t harm you’, is it?

Actually it makes a huge difference. You need to absorb a certain amount of payload in oder to get infected. I found this article[1] on the subject extremely enlightening. [1] https://www.erinbromage.com/post/the-risks-know-them-avoid-t...

One thing unclear from that is how how fast, if at all, accumulated viruses clear out.

Say you need to inhale 1000 of a particular virus to get its disease, and talking normally with an infected person gives you 200/minute, so it takes you 5 minutes to get the disease.

You can get that 1000 by talking 5 minutes with one infected person, or you can get it by talking 3 minutes with one infected person and then shortly afterwards 2 minutes with another.

But what if the gap between those two is longer?

I'd guess that the first 600 you got get into cells quickly and start reproducing, but there are few enough that your immune system is able to handle them. The reason you need 1000 is that is the tipping point where the viruses can reproduce faster than your immune system can handle.

If that's the case, then after you get that first 600, how many you need to get on the next exposure would be 400 shortly after the first, but as the time between exposures increases that would increase.

The model here would be that you have a virus accumulator (you), being filled by exposure events and drained by your immune system, and you get sick if the accumulator reaches some threshold.

This makes me wonder if my approach to shopping during this pandemic is wrong. I've been doing a big shopping trip every 3 or 4 weeks, as opposed to before the pandemic when I'd pop in to the store 3 or 4 times a week and only buy a few things.

Those big trips involve being in the store for an hour or more (and it's not linear--the time to fill my cart is linear in the number of things I'm buying, but checkout time goes up faster because organizing my stuff at the self-checkout becomes harder). If someone else in the store is infected, I could potentially be around them enough to also get infected.

The old small trips only involve a few minutes in the store. If someone else is infected I'm not going to be in there long enough to get an infectious dose from them unless they do something like cough near me. With my mask, and care to avoid other people who are not wearing masks, my realistic risk from an infected person is less than an infectious dose.

If my immune system can clear that out in a few days, then I should be good to go for the next short trip. As long as the prevalence of infected people in my community is low enough that I'm not going to get an infectious dose in a single short trip, this should be a safe approach.

Another question: suppose I get that 600 dose, and no more, so my immune system handles it fine and I don't get sick. Am I spreading the virus during this time, or do I only start spreading after I get an infectious dose worth of accumulated exposure?

Edit: how does acquiring immunity fit in? If I get 60% of an infectious dose and then no further exposure until my body has dealt with that, do I get any immunity or does that only happen if I accumulate enough virus at one time to actually get sick?

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