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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
1/7">https://wwwnc.cdc.gov/eid/artic...
But all is not as it seems...
https://wwwnc.cdc.gov/eid/article/26/10/20-1315_article
1/7">https://wwwnc.cdc.gov/eid/artic...
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
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?
3/7
We don’t have data for 10-15 or 15-20
But this seems like a big and unexpected jump. Why?
3/7
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...
4/7
But wait, there’s more...
4/7
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I have seen unpublished data on this same cohort of children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I have seen unpublished data on this same cohort of children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
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
7/7
7/7
