Covid and Kids

With thanks to @scottleibrand for his regular posts on covid studies.

My wife and I are both fully vaccinated now. If we didn't have kids, we'd be planning our amazing summer of travel. Seeing everyone that we've missed, going to restaurants, and generally being social.

But we have kids. Two year olds. They won't be getting a vaccine for a while yet. What do we do to keep them safe?

Covid in Kids

My naive understanding is that covid is not very dangerous for kids. How true is that, actually?

There are two parts to this question:

  1. How likely are kids to get covid?
  2. How bad will covid be for them if they get it?

Will they catch it?

The good news is that kids age 0-4 are less likely to get covid than adults. That age group is 6% of the population but only 2% of positive covid tests. Compare that with infected people in my age group, which is almost exactly the same as our prevalence in the general population.

On its own, this doesn't necessarily mean children are less likely to get covid from a given exposure. It could be that they're just taking fewer covid tests. It could also be that they are exposed to covid less often than adults.

That said, a meta-analysis published last September finds that those younger than 20 are only 44% as likely to be infected as those older than 20. This trend is even greater the younger the child is. The meta-analysis was on studies of secondary infections, meaning infections of housemates after someone in the house got infected from an outside source. The secondary infection rate is apparently considered a pretty good measure of the person-to-person spread of the disease.

But will they catch it from vaccinated people?

Kids may be half as likely to even catch covid as adults, but what about catching it (at all) from vaccinated caregivers. This is really what I'm interested in, as we'll likely choose babysitters and events based on how vaccinated the adults are.

When the vaccines were first coming out, there was a lot of concern that they'd reduce symptoms but not infectiousness. I'm vaccinated now, but could I still technically "catch" covid and infect my kids without knowing it? Could a babysitter?

Back in April, the CDC talked about a study on around 4000 first responders who got vaccinated. These folks got PCR tests every week, regardless of their symptoms. This let the researchers estimate how well the vaccines block infection, as opposed to just reducing the symptoms once someone is infected. There was a factor of 35x reduction in infections between unvaccinated and vaccinated people. In particular, the vaccine effectiveness (for fully vaccinated folks) was 90% in preventing infection (not just symptoms).

This means that I personally could take more risks without worrying so much about bringing the virus back to my kids. My office (like most in my state) no longer requires masks for fully vaccinated employees. I've still been wearing one since my kids aren't vaccinated, but it seems like I'm not decreasing my kids' risk much by doing that.

Putting numbers on it

These two pieces of information make me optimistic, but it's hard to figure out how to make decisions based on that. Vaccinated baby sitters are a pretty different risk profile than a group day-care (where kids with unvaccinated parents may be common).

I used the microCOVID project to estimate a few different situations that parents may be interested in. I used my local area, so you may want to recalculate these numbers for your area. The risk budget recommended by microCOVID is 200 microCOVIDs per week, which is a 1% chance of getting covid per year. Given children's smaller likelihood of contracting covid in the first place, I divided all the microCOVID values by 2.

While the microCOVID calculator is designed for adults, it's pretty easy to use for toddler interactions. I just assume that the kids are going to be running around grabbing each other, wiping their fluids on each other, and generally being super gross adorable.

As of May 2021, the microCOVID project can't handle assumptions about hanging out with other people who are vaccinated. To get around this, I assumed that the vaccinated people were in the "200 microCOVID budget" category.

  • having a vaccinated baby-sitter over for 4 hours: 35 microCOVIDs
  • having a 4 hour play-date with another kid and their vaccinated parents: 100 microCOVIDs
  • going to daycare with 20 other kids for 40hrs/wk: 1000 microCOVIDs (52000 microCOVIDs/year)
  • having a vaccinated nanny watch your kid for 40hrs/wk: 100 microCOVIDs (5200 microCOVIDs/year)

In other words, sending your kid to daycare would provide a 5% risk of them catching covid in the next year (assuming vaccine use doesn't increase, lots of unvaccinated parents, etc.). The real risk is probably already lower than this.

If you get a vaccinated nanny for 40 hours a week, that would be a yearly chance of covid of around 0.5%. That's assuming one kid, but we have two toddlers. If one gets it, the other will definitely get it as well. So our chance would likely be more like 1% per year (again assuming no change in the prevalence). Likely this probability will decrease as vaccination rates among adults go up.

How bad would it be?

So let's say you send your kid to daycare and they catch covid? How bad will it be for them?

The good news is that covid is usually not very bad for kids (as people have been saying forever). That doesn't mean there's no risk. There have been a couple hundred child deaths from covid over the past year. That's tragic, but it's also not very likely to happen to a given (otherwise-healthy) child.

This paper on outcomes from the first peak in England back in the early part of 2020 gives us some better details. They found a case-fatality rate among children under 16 to be 0.3%. That's the chance of death at the very beginning of the pandemic, given that the kid definitely has covid. I'd bet that number has gone down significantly since this paper was published, as people have learned more about how to treat the disease.

Kids aren't likely to die, but what about other symptoms? A recent paper by Castagnoli et al. shows some epidemiological statistics for the early stage of the pandemic. Most kids were asymptomatic or had only mild respiratory symptoms (like a cough). Honestly, it doesn't sound as bad as when my kids got the normal flu a year ago (which was horrible! Get a fucking flu shot!).

Comparisons to other daily risks

It's easy to look at covid risk numbers and get freaked out. I find it helps to compare against risks that we take every day. For example, what's the risk of travelling cross country to gramma's house? Long road trips expose your kids to risk of car accidents, which are actually a pretty common cause of death in America. We decide that it's totally worth driving across the country so our kids can see gramma. How does that stack up against covid risk?

Wikipedia helpfully summarizes the literature on dying from travel as 1 micromort per 250 miles. If we're driving 500 miles to see gramma, that's a risk of about 4 micromorts for the round trip.

(For those of you not familiar with micromorts, it's a one-in-a-million chance of death. So taking our kids to grammas is a 1 in 200 thousand chance of death. Do that 20 times over the course of their childhood and it's more like 1 in 10 thousand.

Let's convert the microCOVID risks above to micromorts (chance of death) using the 0.3% case fatality rate number. This is likely an overestimate, but I think it'll get us in the ballpark. This ignores the suffering that the kids face if they get sick and recover, but I think it still gives a pretty useful comparison point.

  • having a vaccinated baby-sitter over for 4 hours: 0.1 micromorts
  • having a 4 hour play-date with another kid and their vaccinated parents: 0.3 micromorts
  • going to daycare with 20 other kids for 40hrs in one week: 3 micromorts (156 micromorts/year)
  • having a vaccinated nanny for 40 hours a week: 0.3 micromorts (15.6 micromorts/year)

These all seem pretty safe, if all you're worried about is your kids dying. Every one of them is safer than a cross-country road trip, though the yearly risks for nannying are slightly higher than a single road trip and the yearly risk for daycare is much higher. I personally find all of these risks worth it for the benefits that the activities would bring to my kids lives.

Long Covid

The thing that I really worry about is long-covid. People that had covid, maybe even a very minor case, who then end up with very long lasting health effects.

That epidemiological statistics paper by Castagnoli that showed most kids had only minor respiratory symptoms? It also showed that the kids had "[b]ronchial thickening and ground-glass opacities" in their x-rays. That sounds really bad. Is it going to crop up and harm them later on in life?

Now it may be that long-covid is just one source of various unexplained chronic illnesses that people can get. I would jump through a lot of hoops to prevent my kids from getting something like Chronic Fatigue Syndrome. If the risk of my kids getting a chronic illness from a mild covid infection were high enough, I would absolutely be willing to isolate our household for several more years until they become eligible for the vaccine.

This worry is exacerbated for me because I know two people who had psychotic breaks in the last year that may have been covid related. This is apparently common enough to be a pattern.

The risk of long-covid to my kids is a difficult thing to get a handle on. We're still learning what long-covid even is and how it impacts people, so I'm just going to summarize some of the more informative papers I've seen on it.

The most worrying long-covid evidence I've seen so far is this Nature paper studying the effects of covid on people six months after diagnosis. It compares people who used Veteran's Affairs medical systems, and contrasts long term results of those who did get covid from those who did not. They find that people who get covid had higher usage of pain killers, higher usage of medical therapies in general, and higher incidence of a variety of medical issues (mostly centered around lung problems). This paper also compares 6-month covid complications with 6-month flu complications, and finds the longer-term covid complications to be worse than those for the flu.

William Eden summarizes this as follows:

A 60% higher risk of death, 3% of post-covid cases have lung issues or abnormal blood work, and >1% have some other issues. I'm a little unclear on the difference between hazard ratios (that the paper used) and relative risk, but this seems like a reasonable read to me.

Another study from the UW found that 30% of people who had covid self-reported persistent symptoms (mostly fatigue). That study was pretty small, and only looked at survey data. It does seem consistent with post-viral syndrome, where people who catch a virus can remain fatigued for years afterwards.

A more recent survey in Nature found that 2.3% of their covid-positive population reported symptoms lasting more than 12 weeks. That seems to track pretty well with the results of the Veterans Affairs paper discussed above. This survey also provides evidence that the older you are, the more likely you are to get long-covid (a positive sign for those thinking about the risk to their young children). Other risks that contributed to longer covid symptoms were severe symptoms requiring hospitalization (unlikely in children), and asthma.

A lot of the symptoms described in these papers seem more mild than those in the long-covid horror stories I've heard. I'm also heartened by the fact that most people who have longer term symptoms do seem to get better.

There also seems to be some small evidence that people who get long-covid recover (at least a bit) after getting the vaccine.

Long-covid risks for kids

Based on the above studies, it seems like there's an upper bound of 2.3% for the probability that my kids have covid symptoms more than 12 weeks after getting infected with covid. Given that younger people seem to have fewer issues, I'd be willing to bet that the real probability is even lower. Let's use 2.3% to get some numbers on risks and see what happens.

Instead of inventing some new unit like microLONGCOVID or something, I'm just going to use % chance of getting long-covid. In theory you could calculate DALYs if you really wanted to, but I'm not sure there's enough data on the impact of long-covid to do that effectively.

  • having a vaccinated baby-sitter over for 4 hours: <0.0001%
  • having a 4 hour play-date with another kid and their vaccinated parents: <0.00025%
  • going to daycare with 20 other kids for 40hrs/wk: <0.0025% (<0.12%/year)
  • having a vaccinated nanny watch your kid for 40hrs/wk: <0.00025% (<0.012%/year)


I want to emphasize that the estimates I gave above are based on some very hand-wavey assumptions. I took case fatality rates from early in the pandemic, and they've likely improved since then. I took long-covid incidence from the general population, and evidence is that things are safer for kids. I assumed vaccinated people now had the same risk of getting covid as people on 200 microCOVID budgets at the height of the pandemic (probably a big overestimate).

I'm not using the numbers above to get a real true risk. I'm using them to get an order of magnitude estimate that I can compare against similar risks. From what I'm seeing, there's one main takeaway for me personally: I want to hire a babysitter and go out again!