Thread by @ydeigin

My new essay about the origins of Covid. Where do we stand 2 years later? Personally, I think the case for lab leak has only strengthened, especially given what we have learned from the EcoHealth DEFUSE proposal leak. In particular,

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inference-review.com/article/thunde…

I think it makes a strong case that the PRRA insertion which has created a novel furin cleavage site so uncharacteristic of bat SARS-like viruses was, as Kristian Andersen initially suspected, indeed engineered.

Moreover, it might answer "why proline" and "why PRRA":

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Remember RmYN02 with its PAA "insertion"? I find it quite odd that it is coded by

CCT GCA GCG

codons; and the PRRA insertion in SARS2 is coded by

CCT cgg cgg GCA

i.e. its codons for proline (CCT) and alanine (GCA) are identical to those found in RmYN02.

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In 2021 we've learned about the existence of some BANAL strains out of Laos that showed the same PAA insertion, while other strains had the same RBD as SARS2.

This all dovetails well with the following paragraph from the EcoHealth DEFUSE proposal:

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So I can't help thinking if someone just might have decided to see what would happen if they turned the non-functional PAAR|S furin cleavage site at the S1/S2 into a fully functional polybasic one by changing PAA into PRRA.

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