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Comment by makomk | Hacker News Reader

Like a lot of the Chinese solutions to Covid-19, this is interesting because it really shouldn't work. We know that these kinds of swab tests have a fairly substantial false negative rate - initially from Chinese research, and then I think confirmed pretty much everywhere else - especially when trying to detect pre-symptomatic carriers of the disease. (Also, based on other results elsewhere, I think we'd expect to see a few people out of a Wuhan-sized outbreak testing positive even if they'd long since recovered from the disease and were no longer infectious.)

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Even with a fairly substantial false negative rate, mass testing is incredibly effective for a disease that is contagious while you are asymptomatic.

Suppose the test only caught half of the asymptomatic cases and that anyone with symptoms was properly self quarantining. Then you would stop the spread of the disease by half! and if you had an R0 of 2, then you'd half it to 1.

Obviously, reality isn't as simple as this. It could be thought that these tests have false negatives when the viral load isn't high and when people are less contagious.

The fact that the US hasn't used antigen tests on every person in the country or at least in communities with high amounts of spread should be considered one of the great scandals of our day. A great article on the subject, https://www.theatlantic.com/health/archive/2020/08/how-to-te...

Also, the fact that we don't do mass pooled tests in communities at the beginning of an outbreak like they did in the Xinfadi and later Wuhan outbreaks is also disappointing.

We could have had this under control by now.

No. I don’t want to live in a country where the government can force people to have any kind of test.

It’s one thing to have misconceptions about vaccines and tests but government mandated medical treatment is totally different and completely unacceptable.

It's a little bit more nuanced than that, since vaccines are mandatory in the US. The US government can't force kids to be vaccinated, but it can require that children attending public school be vaccinated. Which seems reasonable - if you want to use public resources, you have to be part of society, which includes protecting other people in the society with you. Most places with a society operate the same way, to different degree, and the only choice is either to opt out and live out in the wilderness, or find individuals who share your stance on, eg, vaccines.

>if you want to use public resources, you have to be part of society,

It’s funny how quickly HN becomes full-fascist as soon as the lightest of real adversity actually arrives.

Why? The government compels you to do all sorts of stuff.

My body my choice.

Your choice can literally kill multiple someone elses during a pandemic.

And how many people can be killed by a government which is mandated to enter the bodies of it's citizens by force? The people should be convinced to take vaccins and medicines (has worked pretty well thus far), but force is a slippery slope I would not like to see the bottom of.

Well, orders of magnitude fewer than 1000/day.

When it's something deadly that affects others, then the difficult question of forcing others comes up. What if smallpox got started again. That kills millions of people. Today most of us in the west don't have personal experience with things like that.

It's like masks. You should be able to make laws that force people to wear masks if there is a deadly disease that will kill other people in large numbers, in my opinion. For those that argue about undue force, what about driver's licenses, taxes, health checks at restaurants, food inspection, building codes, rules on water lines, seat belts, etc? Seat belts mostly just affect people in the car, yet masking and cv19 affects others, so it should be an easier thing to understand the impact.

My guess is our tortured political situation convinces people that somehow the situation is different than these other things.

I think being very specific about language is important here. There's "forcing", and there's "disallowing things if people don't agree to do something".

Forcing would be literally forcibly entering people's homes and testing or vaccinating them against their will, or jailing them or removing them from the country if they refuse. But you could disallow people from entering certain kinds of property or areas if they don't agree to show test results / vaccination status or take a temperature test or wear a mask.

Once a vaccine is officially approved and rolled out, I don't think vaccination should be mandatory for residents of the US, but I also don't think people should be allowed to enter my place of work or education if they aren't confirmed to be vaccinated.

Or maybe freedom is simply the wrong frame for this question. There are others.

Public health. Commonweal. Morality. Consideration for the disadvantaged.

> It's like masks.

It is in fact exactly like masks. You’re not forced to wear one unless you want to be around other people.

Are you sure? Ask your body not to grow old!

Treatment != testing.

I didn't mean to say anything about force, but remember that people have a right to not associate with those who refuse to be tested and, for their own safety, should be given the right to know who has and hasn't been tested or at least the ability to demand someone be tested before they do business with them.

People got used to alcohol tests in traffic

You're right that this could in theory reduce R. The trouble is, it only has that effect for as long as you regularly continue to test everyone, and only within the area where you're carrying this out. The moment you stop it returns to normal. China did this once in Wuhan and once in Beijing, covering roughly one percent of the country's total population each time. That shouldn't do very much at all.

(Also, pooled testing has fairly narrow usefulness. It only really works if the actual positive rate is very low and testing is constrained solely by the ability to process swabs, not by the supply of swabs themselves, the availability of staff and testing locations, or the other processes around testing. This is not generally the case in Western countries.)

You are right that if you stop testing then the R0 goes back up. That is why you test everyone every time there is a new breakout. If keep a breakout from spreading among the community, then the R0 goes to 0. The R0 is probably not very high to begin with in cases where there is a breakout in China because they do very strict lock downs, wear masks, and are in general very careful.

It also helps that anyone visiting China has to undergo 2 weeks of quarantine before going among the community. If you have the disease under control in your community the only threat is outsiders.

Also, you are right that the positive rate needs to be somewhat low for pooled testing to be effective, so that's why you do it at new breakouts before there has been much spread. I had heard that there are, at least in the US, issues with proper swab and reagent shortages, or at least there were delays due to supply chain issues. I thought there were issues with a lack of PCR machines could be wrong. I don't know what the case is in China, though it is clear that pooling is what they did to test people with lower risk of infection (it's in the last article linked in tristanj's comment).

China did a lot of things beside testing. Extremely strict lockdowns in affected areas, a near-total shutdown of passenger transport to and from affected regions and very rapid contact tracing.

China isn't a unique outlier in this respect - South Korea and Singapore followed a similar strategy and got similar results. New Zealand faced a different set of circumstances and used a somewhat different strategy, but they're down to about a dozen cases per day.

Antibody tests like this are very limited. They only detect positive after you've had the virus for several days and they have a significant false negative rate. They are very poor at identifying if this person right here has the virus.

However if what you're doing is trying to assess the prevalence of the virus in a population of hundreds of thousands, or millions, they could be very useful. They will help identify clusters of infection so you can then use the PCR test on known associates to pinpoint cases.

I think this is what the Chinese government did in Beijing, they used mass antibody testing, but PCR testing of everyone in the food market where they knew there were cases.

I think that the commenter you are responding to is not talking about antibody tests but rather rt-pcr test (swab tests) as have been used in China.

You test as much as possible and for any positive you ask the candidate and all associates to self-isolate. Maybe X who is infected gives you a false negative, but if you also test X's mother, husband and son you are likely to get a positive and just isolate the whole household. Similarly a false positive just means you isolate one for no reason - no harm to the community.

One feature that is overlooked from the Chinese response is the rapid contact tracing on a community level through the communist party's Neighborhood Committee. This could be duplicated in the west without authoritarianism through more effective community engagement. For more information, read this article by a New Yorker journalist:

https://www.newyorker.com/magazine/2020/08/17/how-china-cont...

Yep. When I was in China in January, a person from the neighborhood committee called us and asked us whether we've been in contact with anyone from Wuhan, or whether we have any symptoms. Very simple, but contributes to tracing. In contrast, when I went back to the Netherlands 2 weeks later, nobody asked me anything. Even after I called the public health service, they told me I couldn't even voluntarily get tested even if I wanted to. Two months later, COVID-19 cases in the Netherlands surged sky-high.

This has been one of my largest mental blocks on all of this. Per the main reports we see about how this can spread, it feels like that nothing that has worked, should have worked.

Such that I'm sceptical of pretty much all coverage on this now. And I don't think that is a healthy thing to be. :(

> Like a lot of the Chinese solutions to Covid-19, this is interesting because it really shouldn't work.

Are you suggesting China is putting out propaganda?

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