A very interesting study here from South Korea, doing widespread contact tracing to give us a huge data set on secondary attack rates (SAR) for #COVID19 from different age groups

But all is not as it seems...

https://wwwnc.cdc.gov/eid/article/26/10/20-1315_article

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What did they find?

Lowest SAR from children <10y - 5.3% (consistent with other data so far)

Highest SAR from children 10-20y - 18.6%?!

How can it go from lowest to highest in one age bracket?!

2/7

First let’s say that older teens (particularly >15y) do seem to transmit similar to adults, and may be higher risk due to lots of social contacts and less careful behaviour

We don’t have data for 10-15 or 15-20

But this seems like a big and unexpected jump. Why?

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Well a possible explanation is the small numbers of children as index cases. There were only 42 secondary cases from kids aged 10-20, meaning a single super spreading event in a big household from an 18y old could hugely skew results

But wait, there’s more...

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Here is the kicker

I have seen unpublished data on this same cohort of children

Almost every single secondary case from a child index case SHARED the initial exposure

Meaning they probably became infected at the same time, the child just developed symptoms first

5/7

I assume this wasn’t reported here as the authors weren’t able to discern this for all cases in this huge data set

But it’s a total bomb on the conclusion that children aged 10-20 transmit the most. We have no idea if they transmitted to all or none of these secondary cases

6/7

It’s why we must treat these types of study with HUGE amounts of caution, particularly when there are potentially big political implications of rushing to conclusions based on the results

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