Another example of oscillating towards the truth (if you read the latest from @edyong209).
Key open questions: Are kids at the same risk of infection as adults? Once infected, are kids as infectious as adults?
My take on why these questions are so hard to answer 1/8
We know kids are being infected. A small number of kids even get severely ill, but that does not mean kids are infected often nor does it mean they are very infectious. 2/8
Before serology, the best way to detect infected kids was through contact tracing with PCR testing, but that involves a lot of good timing. I’m aware of at least two such studies: from Shenzhen and Guangzhou (our group’s preprint). 3/8
In Shenzhen, they found that kids were being infected at the same rate. We found that kids were being infected less often (odds ratio 0.3 relative to older adults). What’s the difference? Not sure yet! Could be study procedures or in the analysis. 4/8
Our group also tried to assess whether kids, once infected, are less infectious. That is even harder to answer! It is in part based on relative timing of cases in a chain of transmission. Are kids more likely to be the first case? Or the last? We would need more data. 5/8
But we have other kinds of evidence. Anecdotes that we rarely saw household clusters in China that were started by kids. Serology can help us sort this out somewhat since we don’t need to get the timing just right to study who got infected in a household. 6/8
Some studies have looked at viral loads in kids. The hypothesis is that if kids have similar viral loads to adults, then they could be similarly infectious. These studies are helpful, but maybe it’s easier to find kids who are PCR positive for longer? 7/8
This is in no way meant to be a comprehensive summary of the topic (feel free to add more to the comments), but rather my “this is why the science is not settled” take. I’ve seen good evidence supporting all possibilities, so I am reserving judgment for now. 8/8
Addendum: Some have raised the great point that contact patterns for kids have changed with school closures. We want to know if kids are less likely to be infected GIVEN exposure, but they may be less exposed if they are home. Adults, on the other hand, may need to work...
... We can’t just look at prevalence of infection by age without adjusting somehow for exposure. This is where contact tracing studies are useful (condition on contact with a known case). Also, modeling studies that incorporate population-level changes in contact patterns.
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