Can Kids Transmit the Coronavirus?
By: Emily Oster
Tags: Kids, Health, Science, Parenting, Coronavirus

Can Kids Transmit the Coronavirus?

Please, please can we have camp?

Photo: Kawee Wateesatogkij / EyeEm/Getty Images

Pulled from my May 4 newsletter, ParentData

Full disclosure, I spend about 73% of my time obsessing about whether there will be summer camp in Rhode Island. I send borderline appropriate emails to people I work with on virus response, nagging them about this.

I’ve expanded my obsession to neighboring states. Maine seems promising! Maybe we can move there for the summer?! I’m perusing Airbnb like it’s my (fifth) job.

The concerns with opening camps relate to the concerns with opening schools: If we get a bunch of kids together, they’ll spread the virus. As a result, I was pretty excited when I saw a bunch of headlines last week implying that kids can’t spread the coronavirus.

But on the flip side, you have other researchers saying, no, in fact, kids do transmit Covid-19 and opening schools is dangerous. So what is it?

Kids and Covid-19 illness

I’ve already covered kids and Covid-19 a lot and noted that they do not seem to get very sick. There is a Chinese study saying this, there is data from the CDC, and there’s more data from the Netherlands and Italy. Basically, we are pretty clear at this point that serious Covid-related illness is just really, really rare in children.

Kids and viral spread

More complicated is the question of whether kids are viral spreaders. One possible view is that, actually, many kids are infected but they just do not have serious infection. But, of course, they could infect others. So when you get kids together, they’ll spread the virus without you knowing it, and then go home to infect parents, grandparents, and others. I like to call this the “asymptomatic viral bomb theory.”

Another view is that kids are very unlikely to contract the virus at all, and perhaps because their symptoms are mostly mild, they are also unlikely to spread it.

We are uncertain about this because of limited data. And it is clear that kids can spread the virus. There is work, for example, showing that children who are infected have viral loads similar to adults.

But, increasingly, the data points to the second view above: that children are not being an important source of viral spread, largely because they are simply not very likely to be infected.

That data takes largely two forms. First, evidence on the overall risk of infection in kids (not how serious it is, but prevalence). And, second, evidence on whether kids are frequently the source of infection for other people. (In technical terms, are they the “index cases.”)

Let’s start with the first. The key question is whether kids are less likely to be infected than adults. From the data on cases in China and elsewhere, we know they are less likely to be seriously ill. But that’s not the same thing as not being infected. To figure out if they are less likely to be infected, we need to look at a population overall and either test everyone or a random sample of people. If we do that, we can learn what the infection rate is in kids. (Random sample testing is really important!)

There are a few studies like this. One early one was in Iceland. Researchers there tested about 13,000 random people, including 848 kids. Among the whole population, 0.8% of people (so, almost 1%) tested positive for Covid-19. Among children under 10, though, there were no positive cases. This difference was very unlikely to occur by chance.

Data from a single town in Italy which did very widespread screening shows basically the same thing. Kids are much less likely than older people to be infected at all.

It’s not quite as good, since it’s not a random sample, but data from the Netherlands shows that among people who visited their doctor with flu-like complaints over the course of the epidemic, 6.5% of them tested positive for Covid-19. This was as high as 30% in some weeks. However, they detected no cases in people under 20. When kids came in complaining of flu-like symptoms they… had the flu. Not Covid-19.

These three pieces of data suggest that it is not just that kids don’t get seriously ill, but also that they are unlikely to be infected. This is inconsistent with the kids-as-walking-virus-bomb theory.

The other way to understand this is to look directly at whether kids seem to be spreading infection. How? There are a couple of options. One is you could look at cases where a child was known to be infected and see if they seem to spread the virus. Another is you could look in affected groups (say, families) and try to figure out whether kids are often the ones who introduce the virus.

(A third option would be to see what happens when you reopen schools, if that is a big source of infection — we’ll probably see studies like this, but schools are only just starting to reopen in Europe so we do not have that yet).

There isn’t a ton of research on this yet, but where we have it, it again downplays the role of children. In one case, very early in the epidemic, researchers identified a set of cases in the French Alps (all linked to one set of travelers) and the cases included one kid. During the infected period, this kid visited three different schools (it is completely unclear to me why) and had 112 school contacts. None of these contacts were infected.

Obviously this is a single example, but it is worth noting that in the case of adults we have a number of examples (such as the Biogen conference in Boston, some family gatherings in Chicago, one epic party in Westport, Connecticut) where one infected adult spread the virus very widely.

Although it is not yet peer-reviewed, data from Australia is showing similar patterns. In those data, 18 people (nine adults and nine kids) had Covid-19 and were in school contact with others (735 other students and 128 other staff). No staff or teachers developed Covid-19. One primary school and one high school student may contacted Covid-19 from these initial cases. This represents a very low spread rate.

Finally, researchers in the Netherlands have also been shedding light on this. They’ve been following families — preliminary data has 54 families with 239 people — and looking at infections. They have so far found no cases in which the child was the first one in a family to be infected.

The bottom line

Some people have taken the above data to mean “kids cannot spread Covid-19.” This is not right. In principle, they can. They have viral loads, just like adults. Viruses do not know they are carried by kids! If a kid is infected with Covid-19 and they put their hand in their mouth and then they put it in your mouth, there is no reason to think you couldn’t get the virus. (Not that you necessarily would, but that you could.)

However, in practice it seems that infection among kids is simply very unlikely. It’s not that they are infected and don’t know it, it seems like they are just not infected very often. And when they are, it may be that the mild symptoms limit their viral spreading (like with the kid in the French example).

What does this mean for policy, and for families? Opening schools and daycares and camps (PLEASE!!!) is still very complicated since these all involve congregations of adults. But on the plus side, these results indicate that in those contexts, our primary concern should be adult-to-adult transmission, which may be easier to limit.

For families, I think it’s even more helpful. I know many of us are spending a lot of time worrying about spreading the virus from kids to grandparents. The data doesn’t go so far as to say that can’t happen or we shouldn’t be careful, but it dials that down a lot, in my mind at least. This is, in the end, a personal decision for all of us. Good luck with yours.

You can read the original version of my newsletter here.