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Comment by ctoth | Hacker News Reader

Maybe someone here can explain to me how this is supposed to work. Let's assume we have enough tests in the US to test every single person in the country every 3 days, and are contact tracing everyone with a smartphone, and providing smartphones to everyone without.

Now, with all this in place, isn't the best we can do to alert people after they have already been exposed to the virus?

It feels a bit like the safe sex crusaders switching to say everybody can have unprotected sex now, we'll let you know if you catch something, hopefully before you infect your next partner. Which I suppose is more reasonable for the group, but ... as the individual who is expected to actually go out in the world to consume or whatever, this doesn't feel like a viable solution. What am I missing?

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The target is to ensure that each case infects no more than one additional person (‘R<1’).

Each infected person will come into contact with some other people. Testing allows three things—

- first, we can tell this person to stay at home and so stop them from infecting more people;

- second, we can tell the people they have seen to stay at home with good contact-tracing, so that even if they get it they don’t spread it further; and

- third, with enough tests and contact tracing, those who were exposed but not infected don’t have to stay at home.

We are winning so long as R<1, even if there is some chance the infection spreads; we do not need R=0.

The other way of reducing R requiring much less testing and contact tracing is a lockdown. This has obvious downsides. The point of a programme of testing and conyact tracing is that we can turn the cost of avoiding disaster from a lockdown to sticking some things up people’s noses.

edit: typo in first para

So I guess I'm still not seeing this. Can you give me a concrete idea of what this looks like? Let's assume that it is the middle of August and the food situation is still somehow stable, I install my contact tracing app, I get a clean test. Then what? If we miss one person, that one person can still infect an entire office building by coughing in an elevator. Because of the two week incubation period, those people will not know they're infected until at least a couple of days in, even assuming testing daily. We don't yet know how long a person can infect before testing positive, but this amount of time is most likely not 0. If this amount of time is less than 24 hours the person can still make it anywhere in the US by air. If any longer they can make it anywhere in the world. How do we not have constant low-level infection everywhere?

Since this is infectious before symptoms show up, it's basically impossible to eliminate it entirely.

But suppose A starts showing symptoms, tests positive. We can immediately notify B1, B2 and B3 that they need to quarantine, immediately. Before they start showing symptoms. And therefore we're cutting down on the time that they were infectious and spreading. Therefore generation C is only a couple of people instead of dozens. We can notify C generation as well, immediately if we wish. This causes a large quarantine - there are a lot of false positives who are quarantining without being infected - but it would massively reduce the spread. If you can immediately test all of generation B and C, you can perhaps avoid some of the quarantining (assuming a negative is reliable).

Maybe contact tracing misses some, maybe some new infected come from other countries, maybe some people don't quarantine when told. All these things keep the infection going. But it can be held down to a manageable level.

Why would it be? China, South Korea, Hong Kong have all pretty much managed to lower their amounts of new cases down to basically zero, and their society is open for business albeit with social distancing and mandatory mask usage.

The trick is to NOT stop testing once your case count starts going down, instead give the test to everybody that wants one.

A few million spent on 99.9% negative tests daily > a few billion spent on the economy being shut off daily

> But it can be held down to a manageable level.

So I think the word manageable is doing a lot of work here. Specifically, manageable to the hospitals, which is what I believe most people mean when they say this, does not do anything to manage consumer confidence. Which my entire question is about. How do I, as an individual consumer, feel confident enough in the systems set up to go back to some semblance of normal? Learning that my chance of getting infected from going to the grocery store has dropped from 20%? to... 5%? 1%? Whatever the risk is, it needs to be multiplied by the average number of places a normal consumer went to over a week before this outbreak. Which means that I'm still gonna get it eventually, just I might not block somebody else from getting a hospital bed. Which is obviously better than nothing! But I really think people are missing the human aspect of precisely what this entails.

Consider user stories. As a single mother do you still feel confident going out to get groceries knowing there's an n% chance of getting it and bringing it home to your kids? If you die there's no one else to look after them.

The objective isn't to eradicate the virus at this point - that ship has sailed. The goal is to catch enough cases early enough that we can direct just the exposed people to isolate so that we can keep the total patient load at a manageable level without needing to keep the economy on pause forever.

> Now, with all this in place, isn't the best we can do to alert people after they have already been exposed to the virus?

No, the best we can do in that case is treat COVID-19 like a dangerous communicable disease that isn't too widespread for surveillance and do specific quarantines of the infected and exposed, which then vastly limits the possibility that anyone else gets exposed, while not requiring shelter-in-place restrictions for those not already infected/exposed.

That's the whole point of disease surveillance with widespread testing and extensive contact tracing, and why it is key for a general reopening of the economy in the absence of an effective cure/vaccine.

You and I are often in disagreement on here, but not on this!

> Now, with all this in place, isn't the best we can do to alert people after they have already been exposed to the virus?

The goal isn't to "alert" infectious cases, it's to quarantine them so they don't create new infections. Even baring a legal order, someone who knows they are covid-positive is much more likely to stay home and away from others. That reduces the rate of spread, which is ultimate goal.

> but ... as the individual

It's not an individual level solution. There are no individual level solutions (except complete and total isolation I guess). Outbreaks are community events.

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