In normal times, academic research moves slowly. The arrival rate of new information on any given question—Is it healthy to drink coffee, or eat broccoli? Are screens bad for kids?—is fairly slow. Typically, we have time to think through new studies and ask what they add to what we already know.
This is not the case with COVID-19. We know very little about this disease and the virus that causes it, so each new study seems significant. And there are lots of new studies, coming out every day—it’s hard not to feel the study sensory overload, and the speed makes it hard to incorporate any information before new research arrives. The practical consequence is people seem to be grabbing on to each piece of new information as if it supersedes anything we saw before.
Nowhere is this more true than in the discussions of COVID-19, kids, transmission, and schools.
On Thursday, JAMA Pediatrics published a study that had some information on viral DNA in children’s noses. The study was widely covered, with headlines like “New Evidence Suggests Young Children Spread Covid-19 More Efficiently Than Adults.” The general tone of coverage was that this means we cannot possibly open schools. But is that really a reasonable conclusion from this data?
The question of opening schools—whether we should, and what will happen if we do—is a huge one. It involves understanding levels of community transmission, thinking about who will be in school and what protective measures they will take. It involves understanding how the virus is transmitted from student to student, student to adult, adult to student, and adult to adult, specifically in the school setting. There are many, many pieces of evidence we need to bring together to understand this big picture.
So, one element of the big school reopening question is: How much do school-aged children transmit the virus if they are infected? A conclusive answer to this question would impact our understanding of school openings, although it wouldn’t be enough, by itself, to tell us what to do.
If we narrow things further, one part of understanding how much children transmit the virus is to understand the level of virus that infected children carry relative to adults. It is this question—and only this question—that this new study tackles.
To that end, these researchers studied samples from 145 people with symptomatic COVID-19. All of these people (who ranged from less than 1 month to 65 years old) tested positive with a nasopharyngeal swab. When you test someone with a swab, the sample is run through a PCR process. In this process, the viral RNA is converted to DNA, and any COVID-19 viral material is tagged so it can be recognized. The sample is then run through replication cycles to produce enough viral DNA to be recognized. If the sample shows sufficient amounts of viral DNA, it is coded as positive.
When a sample is processed, a positive result is also associated with a CT value, which measures the number of replication cycles that the machine had to do in order to get a detectable amount of virus. A smaller CT value means the sample started with more viral material, since it took fewer replications to produce a sizable account. What the researchers found is that among the 46 children under the age of 5, the replication time was shorter than for older children (5-17) or adults. This means they had more viral RNA material in their nostrils.
That’s it, that’s the study.
So how do we get from this narrow piece of information to the big questions about schools? First, can we extrapolate from viral material to infectious virus? PCR recognizes viral RNA, whether from the whole virus or fragments of the virus. Generally, the presence of viral RNA indicates infectivity, but it’s not exact. Fragmented or weakened virus will show up in this test, but wouldn’t be infectious.
The second, much bigger extrapolation, is from this viral material to transmission. We can speculate, but we do not actually know the relationship between the amount of virus a person carries and how infectious they are. Moreover, this paper is not the only data point we have about how effectively children transmit the virus. A more direct way to study transmission is to look at household transmission varies across age groups: If a 5-year-old is the first person to contract COVID-19 in his household, how many people does he infect? What if a 30-year-old brings the disease home? A large study in South Korea found that children under 10 transmit at a lower rate than other groups (about five percent of their household contacts were infected, compared to 11 percent overall). That study suggests that younger children are not effective spreaders. Another, smaller study of 14 children under 14 in Italy (which has yet to be peer-reviewed) showed transmission to 22 percent of household contacts. These two results are somewhat in contrast to each other, but as the South Korea study is larger, better documented, and has been peer-reviewed, I think at the moment we would favor their evidence.
We want to think about this swab sample evidence in the context of the more direct information on transmission and, honestly, I think we should privilege the direct transmission evidence.
The final step is to ask how this speaks to schools and, here, it seems a very big leap. Among other things, the higher amounts of viral material in this study are seen in children under 5, which is below school age. But beyond that, assuming that, say, 6-year-olds show similarly high levels when they get sick, this is just a tiny, tiny piece of the reopening puzzle. If a study had found that children under 5 did not have any viral material, that wouldn’t have made school reopening safe. And finding that they have a lot doesn’t add much to our understanding of its risks.
Of course, there is value in new evidence, in research. We need to keep learning more about the virus, and this paper helps us do that. But at the same time, we need to be cautious about how much we draw from any given study. And this one doesn’t tell us very much about school opening.