Young kids catching COVID: how much to worry?

post by Steven Byrnes (steve2152) · 2021-04-20T18:03:32.499Z · LW · GW · 20 comments


    confidence, slapdash job. Just putting this up in case other people want to compare notes.
  1. Death from COVID-19:
  2. MIS-C:
  3. Long COVID:
  4. Long-term complications:

Low confidence, slapdash job. Just putting this up in case other people want to compare notes.

Now that all the adults in my family have been (at least partially) vaccinated, my kids will soon be the most COVID-vulnerable members of my family. Therefore it is newly decision-relevant to get a good sense for exactly how worried I should be about them catching COVID-19. This is April 2021, Boston area, two kids under age 7.

Target audience: Frequent readers. Everyone else, go away. This is written for people who treat 1-in-10,000 risks as dramatically, wildly, viscerally scarier than 1-in-100,000 risks, people who understand that “zero risk” is a thing that does not exist in our universe, people who understand that life is full of tradeoffs, including between mental health and physical health, etc. etc. etc.

1. Death from COVID-19:

According to this paper written in August 2020 Fig. 2, the IFR is ~3/100,000 for age 0-4, <1/100,000 for age 5-9. I personally can probably adjust that downward from the known lack of risk factors. So that's very low—not worth sacrificing significant quality-of-life over. (That’s like a month or two out of a reasonable fatality risk budget, I figure—even less since we’re not making decisions that swing the risk of COVID-19 infection all the way from 0% to 100%.)

2. MIS-C:

“Multisystem Inflammatory Syndrome in Children” is a frightening syndrome that can produce severe problems including heart problems, neurological symptoms, strokes, and so on. CDC says (via NYT) that they know of 3185 cases (of which 1% were fatal, but death is already included in the previous section) as of this writing. I'll ignore the possibility that there are more MIS-C cases that the CDC doesn’t know about—this is a pretty serious and well-publicized condition, I presume that most kids with MIS-C are being hospitalized and diagnosed. CDC says most cases of MIS-C were ages 1-14, which is I guess a population of 60M in the USA. I dunno how many kids have been infected with COVID total, but if it’s similar to the prevailing rate (figure 28% including undetected cases), then we’re around 2-in-10,000 risk of getting MIS-C, conditional on catching COVID. (The number of detected cases in kids is disproportionately low compared to the rest of the population, I think, but I’ve always just been figuring that they’re less likely to be symptomatic than adults and therefore have an unusually low detection rate.)

Mayo clinic says “In rare cases, MIS-C could result in permanent damage or even death.”, which (accidentally) implies that almost all the time, kids who get MIS-C fully recover without permanent damage. That’s not a great source, but whatever. Also, this says that 7/7 MIS-C cases at a particular hospital were “fully recovered”.

So I figure, conditional on a kid catching COVID, there’s a 2-in-10,000 risk of getting MIS-C, going through a somewhat terrifying ordeal, but eventually fully recovering. And, there's a, I dunno, 1-in-100,000 risk of permanent problems. Again, combine that with the fact that I’m not making decisions that swing the risk of COVID-19 infection all the way from 0% to 100%, and I find this a pretty much acceptable price in cases where I’m spending it on real benefits in my kids’ mental health and quality-of-life. Unless my numbers are wrong of course. So I'm pretty much ignoring MIS-C too. The next two categories seem much worse than that.

3. Long COVID:

Children with long covid” (New Scientist, Feb 2021) says “Evidence from the first study of long covid in children suggests that more than half of children aged between 6 and 16 years old who contract the virus have at least one symptom lasting more than 120 days, with 42.6 per cent impaired by these symptoms during daily activities.” What??? 43%? No way. That’s way too high. This article calls it rare. 43% is not rare.

The 43% statistic comes from Preliminary Evidence on Long COVID in children. It seems like a helpful article but I don’t know what to make of the selection bias. Where exactly did they get these kids? “This cross-sectional study included all children ≤18 year-old diagnosed with microbiologically-confirmed COVID-19 in Fondazione Policlinico Universitario A. Gemelli IRCCS (Rome, Italy).” That should disproportionately sample sick kids, and especially severely sick kids, right? So I’m going to ignore that.

The New Scientist article also says “The UK Office for National Statistics's latest report estimates that 12.9 per cent of UK children aged 2 to 11, and 14.5 per cent of children aged 12 to 16, still have symptoms five weeks after their first infection.” That’s this link. I’m guessing that the population here is "initially-symptomatic kids" as opposed to "all infected kids". So divide by 2 or 3? And not all of those 12.9% are catastrophic. Some may be kids who are easily-fatigued for 5 weeks then recover, which kinda sucks but isn’t that big a deal. I dunno, figure, conditional on a kid catching COVID-19, 2% chance that it’s, like, a really really long and miserable slog that everyone will deeply regret. The rest of the time it's at worst in the ballpark of adding up 1 unusually severe flu + 1 broken leg—lots of pain, hassle, doctors visits, medical bills, missed activities, and so on, but not worse than that. Life goes on.

4. Long-term complications:

Maybe you catch COVID as a kid and then there’s a 1% higher risk of heart disease decades later. Or something else. How would we even know?

My general impression is that kids’ bodies are generally good at recovering and rebuilding themselves over time. But that’s not really based on anything. An example in the opposite direction is polio: I guess polio kills nerve cells in a way that’s unrepairable, and which gradually gets worse and worse over decades after apparent recovery? Is the nervous system unusually hard to repair?? Because, um, COVID often impacts the nervous system too, right?! Yeesh.

I have no idea, I’m out of my depth here.

I guess I'll say 1% chance of a big-deal long-term latent problem, conditional on catching COVID-19. That's not really based on anything, but I need a number because I have to make decisions and weigh tradeoffs. Happy for any input here.


So, conditional on a kid catching COVID, I guess I'm currently thinking that I should mainly be weighing a ~2% chance of a miserable months-long ordeal until they recover, plus (overlapping) ~1% chance of a big-deal long-term latent problem that will show up later in life.

OK, I guess when I multiply everything out right now…

(UPDATE 2 MONTHS LATER TO ADD: When I wrote this list below, COVID prevalence in my region was 16× higher than it is today. So I'm obviously being more relaxed now. Different regions are different; I suggest using the microcovid calculator.)


Comments sorted by top scores.

comment by Alexei · 2021-04-20T19:16:28.933Z · LW(p) · GW(p)

Thank you for looking into this and posting about it. This question has been on my mind a lot.

Replies from: steve2152
comment by Steven Byrnes (steve2152) · 2021-04-20T20:58:42.742Z · LW(p) · GW(p)

You're welcome but I hope you're not taking my word for anything. Note the warning at the top :-)

comment by Jeff Rose · 2021-04-25T14:58:17.303Z · LW(p) · GW(p)

Interesting.  We are in somewhat the same boat. Fully vaccinated adults with a two year old.  I think where we come out is as follows.  

(1)  The risk to kids of COVID over the short term are clearly lower than for adults.  Over the long term, it is presently unknown.  

(2) It is highly likely (>90%) that we will be able to vaccinate young children by next year, so any risk reducing measures we take will be temporary. (Also, see (5).)

(3)   The risk from outdoor activities and from vaccinated people are very low.  Therefore, we are fine with outdoor activities masked or not and with socializing with fully vaccinated people.

(4) There are limited gains from indoor activities with unvaccinated people, so we will not bring our daughter indoors with unmasked unvaccinated people or unnecessarily indoors with people whose vaccine status is unknown.

(5) COVID prevalence here is dropping, whether for reasons of increased vaccination or otherwise.  If, due to increased vaccination, those rates stay down, we can relax these restrictions.

comment by hold_my_fish · 2021-04-24T05:42:02.549Z · LW(p) · GW(p)

This seems reasonable, but I wonder whether "long-term complications" might be a bit underrated. It seems like there are a lot of viruses that have long-term effects or other non-obvious consequences. (I should add that I'm not a biologist, so this is not an informed opinion.)

The example I'm most familiar with is chicken pox causing shingles, decades later from the initial sickness. In that case, shingles is (I think) typically more severe than the original sickness, and is quite common: 1 out of 3 people develop it in their lifetime, according to the CDC.

Other examples that come to mind are measles erasing immune memory (which IIRC wasn't known until recently) and, though not a childhood illness, HPV causing cervical cancer.

Each of these examples has some big differences from SARS-CoV-2, but there isn't much experience with severe coronaviruses, so I don't know how to do better. Maybe the ideal would be to go through a list of reasonably well-understood viruses and check what proportion have known long-term effects or non-obvious consequences (and the rate).

We can get a lower bound from chicken pox and measles. If there are 10-20 common childhood illnesses (based on a quick search), then, using 2 as the numerator, at least 10%-20% of them have consequences that are not immediately obvious. If we go with the 1/3rd rate for shingles (since I don't know for measles), that would translate into a 3%-7% lower bound for covid.

Would I go with a >3% estimate of serious long-term effect or non-obvious consequence from covid to a kid that catches it? A persuasive counterargument that comes to mind is that the immediate experience of covid is less severe to a kid than chicken pox or measles, which would suggest that non-immediate effects are also less severe.

All-in-all, my confidence is extremely low, but hopefully this gives some food for thought.

Replies from: steve2152
comment by Steven Byrnes (steve2152) · 2021-04-24T21:07:41.330Z · LW(p) · GW(p)

Yeah thanks!

I guess was thinking that kids who don't get bad cases at the time are unlikely to have long-term effects. I think polio is like that. In particular, I assume that only the bad COVID cases get into the nervous system, where I'm especially concerned. So that's how I got a lower number. But I dunno either :-)

comment by limestone · 2021-04-23T15:35:52.598Z · LW(p) · GW(p)

I've also been looking for posts like this, slapdash as you may feel it is (but well-organized!) I have been considering going to an outdoor cookout including our <10yo kids where maybe 25% of the adults are vaccine-hesitant and won't have masks. microCOVID didn't seem to have enough options for me to model this type of group, but I just realized I could do a calculation by only including the number of people likely to be unvaccinated. We decided to go with our kids masked (either surgical or filtered) and distanced, but it's a big step as the first event we will have attended outside our bubble.

comment by Gunnar_Zarncke · 2021-04-21T06:34:59.454Z · LW(p) · GW(p)

Overall, this sounds a lot like flu side-effects:,failure%2C%20asthma%2C%20or%20diabetes. 

I'm not saying "it's the flu". I'm saying that if Covid becomes another flu-like childhood disease, as Scott Alexander predicts, then we should expect comparable long-term effects. The question might be how much that changes the baseline of such conditions overall. 

comment by tkpwaeub (gabriel-holmes) · 2021-04-24T01:42:24.817Z · LW(p) · GW(p)

Keep an inventory of the new BinaxNow home tests and have guests pay for them.

comment by cistran · 2021-04-21T16:33:17.670Z · LW(p) · GW(p)

Have you looked into risks improper mask wearing poses? Things like moist dirty masks and associated  increased chance of bacterial infections and aggravation of acne. Children wearing masks in school are especially at risk of wearing masks improperly.

Replies from: steve2152
comment by Steven Byrnes (steve2152) · 2021-04-21T17:42:36.065Z · LW(p) · GW(p)

Those don't seem to be worth worrying about, so far as I can tell. It seems like they are rare (or maybe nonexistent) (insofar as I haven't heard of any such issues through friends or family or the news), and they also sound like not that big a deal even if they do happen. You can tell me if I'm missing something.

Replies from: cistran
comment by cistran · 2021-04-21T19:12:55.826Z · LW(p) · GW(p)

Rare compared to what? I haven't seen actual studies but my anecdotal observations show about one person in ten wearing visibly moist and soiled mask. This maybe area dependent, so your observations may be different, and they are what matters. But kids are generally not as fastidious as adults. The main worry for young kids is how much more likely is the bacterial throat infection if the mask they are wearing is dirty. Here is a relevant article (

Acne aggravation from mask wearing is well-documented, but your kids are too young for that problem. 

Replies from: steve2152, pktechgirl
comment by Steven Byrnes (steve2152) · 2021-04-21T19:38:45.180Z · LW(p) · GW(p)

Sorry, I meant "negative consequences of mask-wearing are rare", not "wearing moist and soiled masks is rare". I've worn moist and soiled masks from time to time, and nothing bad has happened to me so far, except perhaps looking a bit unprofessional :-)

And I meant "rare compared to 100%". Like, if even 1% of mask-wearers got a throat bacterial infection, that would be millions of throat bacterial infections in my country, 50,000 in my state, hundreds in my town, and probably at least one or two among my friends and family and acquaintances. So if that's actually a thing that's happening at a 1% rate, I think I would have heard something about it by now. Unless those infections were really not a big deal, such that they don't rise to the level of even being worth mentioning to your friends.

(How many people do you personally know who have gotten a bacterial throat infection from mask wearing? How bad was it? Were they hospitalized? How many days of work did they miss?)

So I figure that bacterial throat infections from mask wearing is either <<1% likely to happen, or it's really not a big deal when it does happen, or (most likely) both.

Replies from: cistran
comment by cistran · 2021-04-22T06:40:24.693Z · LW(p) · GW(p)

But it is a bigger deal for children. Children can get complications from throat infections. 

You were looking at problems with one in ten thousand odds, but you don't have ten thousand acquaintances of acquaintances, so it is unlikely that you would get second hand reports of problems with these odds. 

You have even less acquaintances with children, perhaps no more than a few hundred, so even problems with odds of one in a thousand are unlikely to reach you via second hand reports.

Replies from: steve2152
comment by Steven Byrnes (steve2152) · 2021-04-22T11:30:39.054Z · LW(p) · GW(p)

What are the complications? Death? Weeks in the hospital? Lifelong complications?

I suspect that if there was even 1-in-100,000 chance of that kind of consequence from regularly wearing masks, I would have heard about it by now. But if you have a reference to actual incidents (not just speculation that it's possible, but actual people who had these kinds of very very serious problems), I'd be interested to see that.

I want to consider possible impacts of my decisions that are either (1) common, (2) rare but catastrophic. MIS-C is not super catastrophic, but it's fatal if you're not promptly hospitalized, and occasionally fatal even if you are, if I understand correctly. So it enters into consideration, despite being rare. And even so I wound up declaring that MIS-C risk is too low to be decision relevant. I have a hard time imagining that wearing a mask will lead to consequences anywhere remotely as serious as MIS-C. So it wouldn't enter into my consideration unless it was very common, like >1%.

comment by Elizabeth (pktechgirl) · 2021-04-22T22:39:08.075Z · LW(p) · GW(p)

The linked article is low quality. It proposes a mechanism but gives no evidence for its frequency or severity or even if it actually happens at all.  It is clearly not doing cost/benefit calculations.

Overall you seem to be putting the burden on Steven to prove that there isn't a risk to masks, rather than doing anything to demonstrate that there is. I agree with considering the costs as well as benefits of masks and would love to see real data on the costs of masks, but this is an unfair burden to put on Steven in particular as a reward for a pretty useful write-up.

Replies from: cistran
comment by cistran · 2021-04-23T17:31:32.423Z · LW(p) · GW(p)

Nobody seems to be doing any cost/benefit calculations on masks. Particularly when it comes to fully vaccinated people wearing them. Why are we not doing it, especially the cost part? The benefits at least are tractable. But the costs are not easy to calculate. Obviously they are bigger than the cost of masks themselves, time it takes to properly take care of them one way or the other, and the cost of their disposal.

Replies from: steve2152
comment by Steven Byrnes (steve2152) · 2021-04-23T18:59:03.460Z · LW(p) · GW(p)

Hmm, I think for me the dominant cost of masks is that they're mildly annoying. That's a much bigger cost for me than the monetary price or the time spent laundering them or whatever.

I endorse not wearing masks when they provide zero or infinitesimal benefit. Like, where I live, there's a rule that people walking alone outside need to wear a mask. That's a really dumb and annoying rule.

I expect to be doing more stuff without masks, and more stuff period, when I'm fully vaccinated, and so are my friends, and when the prevailing COVID rates in the community are much lower than they are now. Can't wait, and I think it won't be much longer, in my community anyway. :)

Replies from: cistran
comment by cistran · 2021-04-23T20:06:39.146Z · LW(p) · GW(p)

Have you considered the cost and benefit of masks worn by your six years old child?

Is he getting bigger benefit than you?

Are his costs smaller than yours?

Replies from: steve2152
comment by Steven Byrnes (steve2152) · 2021-04-23T21:17:16.085Z · LW(p) · GW(p)

My kids really don't mind wearing masks. They really just don't care, they don't even think about it. Sometimes we'll get home and they'll just forget to take their masks off! Like, for a really long time! They just got used to wearing masks when going out, pretty quickly into the pandemic. Young kids are adaptable. :)

I'm not really sure what your question is getting at. There's no sense in directly comparing my need for a mask to my kids' need for a mask. It's not like we only own one mask and need to fight over it... 

For what it's worth, it wasn't my decision, but I am very happy that everyone in their school has to wear masks indoors. The benefit of reducing in-school COVID spread seems to me to overwhelmingly outweigh the (trivial) costs of making kids and teachers wear masks. I think that the prevailing COVID rates in the community would need to be very low indeed—maybe 10× or 100× lower than today—before I would endorse having kids in school stop wearing masks, at least until there's a vaccine available for kids.

Replies from: cistran
comment by cistran · 2021-04-24T13:41:26.706Z · LW(p) · GW(p)

How many cases of COVID were detected in your child's school in one year?