What the heck do we know about kids and COVID-19 transmission?

Families/Kids Infection and Spread

A: We STILL need more data. But so far there is decent evidence that:

1) kids (especially younger kids) are less likely to be infected (yay!).

Less solid but suggestive evidence that:

2) kids *may* be less likely to transmit SARS-CoV-2 to others.

Note that says LESS likely, not that they DON’T transmit!

How do we know this? We know that children are under-represented in case numbers all over the world, but in theory this could be because of mild or asymptomatic illness that makes them less likely to be tested.

To rule this out, some studies have tested all members of infected households. Using PCR tests for current infections, kids (esp. ages 0-10) seem about half as likely to become infected as adults.

But if kids are often asymptomatic, they might have already been infected and recovered, and thus less likely to test positive to a PCR test, right?

YES! To get at this, we have some emerging serology evidence. Serology (blood) tests for the presence of antibodies and thus previous rather than current infection. A population-based sample from Geneva found that only 0.8% of children ages 5-9 had positive antibodies, compared to an overall seroprevalence of 10.8% in the population.

What about transmission? This one is trickier to pin down, since children may be more likely to be asymptomatic and thus may be less likely to be identified as an “index case” in a household. We have anecdotal evidence from early cases among children that onward spread seemed minimal, but unfortunately, we don’t have any hard data that has followed many kids over time as of yet.

Schools were already closed during many of these early household contact tracing studies, meaning kids had less exposure and opportunity to transmit to their families than they normally would have. We have some evidence that infected kids may have lower viral loads than infected adults, but how this translates into infectiousness is not known.

How infectious kids are remains one of the most important outstanding COVID-19 questions, and hopefully we will have some better data soon as schools have reopened in some countries.

Emerging data is a mixed bag, with Denmark re-opening schools without much incident, but some infection flare ups and clusters after classes resumed in Israel (note the major cluster was in a middle & high school, consistent with other evidence that infection risk for tweens and teens more similar to adults, while lower for younger children).

Until we have more data, it’s prudent to assume that kids CAN transmit, even if less effectively, and to plan individual, family, and community risk reduction accordingly.

We will be writing a lot more this week about the difficult questions around school re-openings: stay tuned!!

Some helpful summaries of current knowledge on kids and COVID-19:

Don’t Forget The Bubbles – The Missing Link?

Don’t Forget The Bubbles – Evidence Summary

Stat News