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Comment by Taniwha | Hacker News Reader

However there already exist real people in the world who have had Covid twice, and who reportedly have had a much tougher time the second time around.

This study helps us put some bounds on how many people this might happen to (assuming there are no mutations to the virus) but it doesn't rule it out completely, because of the prior existence proofs

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Most reinfections are milder the second time.

The early Nevada case involved a relatively younger person who caught it once. Then they caught it again while caring for a parent who also had it and was hospitalized. The case was confirmed by PCR analysis of the samples that were taken combined with validating that the samples had the subjects DNA in them.

But they likely had a very mild initial infection and being young they fought it off with mostly an innate immune system response and didn't generate a lot of antibodies or adaptive response.

Then when their parent got sick (in the same household) I would bet money the cared for that parent taking little to no precautions believing that their prior infection granted them survivor-island-style invincible immunity to disease (which is how most people think the immune system works). They likely got a whopping large viral dose which (probably combined with a bit of bad luck) is what caused the second infection to be severe and require hospitalization.

And due to selection effects that unusual case bubbled up to the top early because it was someone in the hospital with covid who had positive evidence that they'd caught it 3 months earlier. A lot of people with mild covid both times would never have landed into a study and the clinicians wouldn't have bothered with genetic sequencing.

I got covid twice.

10 months separated the first and the second infections.

Both were mild, the second was worse (English variant).

Now I know two things about you: 1. you got covid twice 2. you weren't part of this study

This is only one data point. My partner also got the covid twice, at the same time obviously.

The important point here is that we got re-infected almost a year later with a variant.

From my experience, it looks like the flu.

Were you tested both times to confirm?

If this is rare enough, it could fall into the false positive rate of the COVID test they've previously done (i.e. while the test said they had COVID, they didn't)

Could be - but the case I remember reading about involved hospitalisation.

Remember that immunisation makes antibodies but only provides something like 50-95% protection (depending on the vaccine) - it's not surprising that actually catching it does the same thing

The tests are designed to have high false positives because they have to bias toward few false negatives and there are no perfect tests. What gets me is that the negative result is the one bearing meaningful information but not the positive result, yet everyone mistakenly talks about positives as if they are far more informative than they actually are.

I'm not sure what test you have in mind, and I'm guessing that such tests with high false positive bias might exist, for example the antibody tests. It's very difficult to get a genuine false positive with a PCR-based test: whatever you're reading out should have the same sequence as the part of the virus you're sequencing. The only reasonable way to get a false positive is that you contaminate the sample, but I don't think that the possibility of contamination is part of the design in any of the commercially available tests.

There are essentially zero false positives with the PCR test. Only through sample contamination.

Certainly the case with the PCR test, because it is so sensitive. It can detect Covid fragments at such a low level that no symptoms would show and no adaptive immune response would arise. That's not enough Covid to generate memory and immunity.

You could be PCR tested positive, while experiencing a cold or flu (which you would now understandably think were Covid symptoms), but would not have immunity for a future, larger infection from Covid.

Though statistically unlikely, it's bound to happen sometimes.

> However there already exist real people in the world who have had Covid twice

Sure, but these things are rare enough that it can be only people with a wonky immune system or some other exotic condition.

From a family member who works with Covid response (in India, where you have a large enough sample size), repeat infections are less likely and tend to be mild. But they are neither rare nor limited to people with exotic conditions.

Health policy is determined by probabilities, not possibilities.

Health policy (not uniquely) is determined in large measure by politics.

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