I don't dismiss it completely, but I follow the virology communities' opinion that a leak is unlikely, since I can't evaluate the information myself, e.g. the Furin cleavage site enabling the virus to jump to humans evolved naturally. What the fuck is a Furin cleavage site, actually? Fuck if I know. Fuck if anyone here knows. (Besides Raist, who is a virologist iirc.)
Please. I'm a molecular immunologist, not a dirty virologist peasant
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Furin is an enzyme that cuts proteins at very specific sites that have a well defined sequence. Furin sites in the Spike protein isn't uncommon in coronaviruses (or proteins from other viruses), but what makes people raise an eyebrow is:
- the couple of coronaviruses that are the most closely related overall to SARS-CoV2 (thus the most likely to be its progenitors, if we assume that it's 100% "natural") don't have a furin site.
While not strictly impossible, the emergence of that particular sequence from scratch has a rather low probability, and the alternative possibility that one of those couple "progenitor" viruses recombined in the wild with another one that does have a furin site would be very likely to look like something quite different from SARS-CoV2.
- The exact nature of this particular sequence (at the genomic level) is a bit odd, again the probability for it to have appear naturally is very low.
None of this is an absolute "proof" that it was artificially derived for research, and someone fucked up, but at the same time its origin are not clear at all, and there is to date no definite "it evolved from this exact bat (or other reservoir) virus". Something that is usually identified relatively quickly, including back when the methods used were nowhere near as cheap, quick, and robust.
tl;dr: