Aleks pointed me to this article, which reports:
Epidemiologic data consistently show strong protection for young children against severe COVID-19 illness. . . . We identified 3,126,427 adults (24% [N = 743,814] with children ≤18, and 8.8% [N = 274,316] with youngest child 0–5 years) to assess whether parents of young children—who have high exposure to non-SARS-CoV-2 coronaviruses—may also benefit from potential cross-immunity. In a large, real-world population, exposure to young children was strongly associated with less severe COVID-19 illness, after balancing known COVID-19 risk factors. . .
My first thought was that parents are more careful than non-parents so they’re avoiding exposure entirely. But it’s not that: non-parents in the matched comparison had a lower rate of infections but a higher rate of severe cases; see Comparison 3 in Table 2 of the linked article.
One complicating factor is that they didn’t seem to have adjusted for whether the adults were vaccinated—that’s a big deal, right? But maybe not such an issue given that the study ended on 31 Jan 2021, and by then it seems that only 9% of Americans were vaccinated. It’s hard for me to know if this would be enough to explain the difference found in the article—for that it would be helpful to have the raw data, including the dates of these symptoms.
Are the data available? It says, This article contains supporting information online at http://www.pnas.org/lookup/suppl/doi:10.1073/pnas.2204141119/-/DCSupplemental but when I click on that link it just takes me to the main page of the article (https://www.pnas.org/doi/abs/10.1073/pnas.2204141119) so I don’t know whassup with that.
Here’s another thing. Given that the parents in the study were infected at a higher rate than the nonparents, it would seem that the results can’t simply be explained by parents being more careful. But could it be a measurement issue? Maybe parents were more likely to get themselves tested.
The article has a one-paragraph section on Limitations, but it does not consider any of the above issues.
I sent the above to Aleks, who added:
My thought is that the population of parents probably lives differently than non-parents: less urban (so less exposure), perhaps biologically healthier. They did match, but just doing matching doesn’t guarantee that enough of the relevant confounders have truly been handled.
This paper is a big deal (1) because it’s used to support herd immunity and mass infection; (2) because it is used to argue against vaccination; (3) because it doesn’t incorporate long COVID-19 which can be caused even by an asymptomatic infection.
For #3, it might be possible to model the impact, based on what we know about the likelihood of long-term issues, e.g. https://www.clinicalmicrobiologyandinfection.com/article/S1198-743X(22)00321-4/fulltext
Your point about the testing bias could be picked up by the number of asymptomatic vs asymptomatic cases, which would reveal a potential bias.
My only response here is that if the study ends on Jan 2021, I can’t see how it can be taken as an argument against vaccination. Even taking the numbers in Table 2 at face value, we’re talking about a risk reduction for severe COVID-19 from having kids of a factor of 1.5. Vaccines are much more effective than that, no? So even if having Grandpa sleep on the couch and be exposed to the grandchildren’s colds is a solution that works for your family, it’s not nearly as effective as getting the shot—and it’s a lot less convenient.
Looking at the Israeli age-stratified hospitalization dashboard, the hospitalization rates for unvaccinated 30-39-olds are almost 5x greater than for vaccinated & boosted ones. However, the hospitalization rates for unvaccinated 80+ is only about 30% higher.
It is interesting to read these posts now that Fauci and the FDA have come out and said there is no widespread belief these vaccines have any meaningful impact on infection/transmission.
Also, obviously you can get herd immunity from infection, but it wanes after a few months to years (roughly proportional to the severity of the illness). That is just like expected from observing similar viruses.
 I’ll find the recent discussion in the comments here if anyone asks.
I’m interested in the discussion. Could you provide a reference?
The big question is why so many politicians and media figures held this fringe belief that was contrary to all experience with similar viruses and verified in the preclinical animal trials.
Are parents more likely to live in multi person households? Almost by definition by being parents because they have the children with them plus probably more likely to be partnered.
– Is being tested individually independent of other people in your household being tested?
– Is being tested individually independent of someone in your household testing positive?
– Is testing itself independent of being positive?
I think the answer to all three is probably “no.”
With an airborne virus and also based on my own family, I suspect that if one person gets tested then other people in the family get tested.
I suspect that if someone in your household tests positive that then you get tested.
I suspect that people with symptoms are more likely to get tested.
Oh and some people test all the time, symptoms or not, are they controlling for that? And some people who test negative test several days in a row until they test positive.
Also they don’t seem to control for number of children.
The abstract of the Solomon et al. paper ends with “This epidemiologic signal suggests endemic coronavirus cross-immunity may play a role in protection against severe COVID-19 outcomes,” which seems plausible enough. According to Google Scholar three other papers (including a second paper by Solomon et al.) have found the same association.
I’m very wary of reverse engineering the biology of the virus from interpreting epidemiogocal data.
Not to say that it’s not worthwhile to look at those data, but without lab-based empirical biological evidence (regarding the mechanism of cauality) there’s just soooooo much uncertainty.
As I recall, fairly early on in the pandemic there was a lot of speculation about cross-immunity from infections from other coronaviruses providing immunity for COVID, and most virologists seemed to think there might be some protection from infection but not likely much regarding security of disease outcomes.
Of course, those virologists could have certainly been wrong – as I said that was fairly early on. But thia study seems to suggest pretty much the exact opposite?
I’m all for reserving jisefemsnt until empirical, lab-based data are provided and/or these same sort of findings are found across many studies.
(I say this as someone who lives with a
germ factory5 year-old, where my partner and I are among the few people I know who have never had an identified COVID infection, let alone a serious infection.)
“security” of disease outcomes = severity of disease outcomes.
Now that I think about it more…
After re-exploring my memory cells, I now think the virologists were saying that (T cell based) immunity from previous infections with other coronaviruses might help provide protection against severe disease but not likely against infection…. So not the opposite of this study’s findings but not entirely consistent either. I’ll see if I can find some links from 3 years ago.
I found a link – from August 2020….
7/ We SPECULATE that it is conceivable that these T cells may potentially reduce COVID-19 disease severity, based on things we know about flu and T cells.
10/ Additionally, even if our most optimistic speculations about crossreactive T cell memory were found to be correct, it would mean that just as many people would get infected with SARS-CoV-2, but fewer would become severely ill and die from COVID-19.
The context was that some people (er….mostly rightwingers who were talking out of their asses) were postulating that relatively low infection rates in Asia were explained by “herd immunity” with a ridiculously low population infection rate because of previous exposure to other viruses.
> My only response here is that if the study ends on Jan 2021, I can’t see how it can be taken as an argument against vaccination.
You’re making a mistake if you’re expecting commonly found arguments against vaccines to be logically coherent.
“My first thought was that parents are more careful than non-parents so they’re avoiding exposure entirely. ”
Most countries restarted schools fairly quickly after the first wave, so i’m not sure this is true… at least looking at colleagues/friends in my age group the ones who got a covid infection usually caught it through their (young) kids, while the childless didn’t get sick at all. Their kids are the disease vector.
I can also imagine that having kids exposes you to many more bugs (again… my colleagues/friends/family with children commonly complain about “my kid got sick, then I caught it too”), so their immune response might be stronger too!
I’m not quite clear on the controversy here. Summarizing from the abstract and intro:
1) children are typically exposed to endemic corona viruses
2) children have a very low incidence of severe COVID-19 cases
thus: the exposure to endemic coronaviruses appears to provide some immunity against severe COVID-19.
In the study data, adults that have children have lower rates of severe COVID than adults without children.
Thus the authors speculate: parents living with children, who carry and/or are exposed to endemic coronaviruses, leads to exposure of the parents to endemic corona viruses as well, granting them some immunity to severe COVID.
I’m not sure why this needs to be explained away with confounders or other comparison problems. It makes sense. Maybe there are problems with the study – nothing is apparent to me at first glance – but it seems like a tentatively sound result with a reasonable mechanism, and a result that would ideally be investigated further for confirmation.
Nobody is saying it doesn’t make sense. Of course it makes sense.
Nobody is trying to “explain it away.”
Just because it makes sense doesn’t necessarily mean it’s true. If we accepted every theory that ”makes sense”, there would be no such thing as science and no need to collect data.
Theories that make sense are often wrong, although not as often as theories that don’t make sense!
Every theory and every study should be examined for weaknesses. You should always ask “is there any way this could be wrong?”
Statistician finds red object. Spends two years taking measurements and analyzing data to ensure the object is red. Result: data inconclusive. Its possible the item may not be red.
Statistician finds blue object. Spends two years taking measurements and analyzing data to ensure the object isn’t red. Result: data inconclusive. It’s possible the item may actually be red.
Idiot sees a theory that makes sense to him. Sees some data that seem to support it. Doesn’t bother questioning whether there could be something wrong with the data or the theory. Idiot assumes theory is confirmed to be true.
I thought it was reasonably well established that the severity of a Covid case was influenced by the initial viral load. And that the viral load in children always remains low.
So it would be quite surprising if being infected by a child led to as severe of cases, on average, as being infected by an adult.
It’s possible, sure, and the data do seem supportive, provided we assume the authors collected and analyzed it appropriately (always a big if). But I see the specter of multiple comparisons–huge dataset, a good amount of variables, and no reason to believe this particular finding was not HARKed.