Thread by @MichaelWorobey

Here I explain why I (continue to) think that a zoonotic origin of SARS-CoV-2 is more likely than a lab leak scenario - even though I signed 'The Science Letter'. 1/

https://twitter.com/JohnsHopkinsSPH/status/1417575068041949187

I am a co-author, with @jbloom_lab, @DavidRelman and others, of a widely discussed letter in Science Magazine that argues that both a zoonotic origin and a lab-linked origin are important to consider. 2/
science.sciencemag.org/content/372/65…

I'm also a co-author, with @edwardcholmes, @arambaut, @angie_rasmussen, @stgoldst, @robertson_lab, and others, of a recent preprint that argues that a zoonotic emergence is the more likely scenario. 3/
zenodo.org/record/5075888…

(My co-author @angie_rasmussen has already done a superb job of summarizing the main arguments). 4/

https://twitter.com/angie_rasmussen/status/1412864854990503944?s=20

Why am I on both papers? The answer is *not* that I've undergone a dramatic conversion - I've always thought a zoonotic emergence was more likely than a lab leak.

In light of recent evidence/thinking I simply view it as *even more* likely. 5/

I wanted to clarify this since a couple of very good recent press articles may leave the impression that as a co-author of the Science letter I used to think the lab leak scenario was more likely. These include one by @carlzimmer 6/
nytimes.com/2021/07/09/sci…

And one by @FoodieScience (in both cases I failed to point this out to the journalists, so it is my fault, not theirs). 7/
npr.org/sections/goats…

So, what's moved my thinking? First, a preprint by Dr. Shi Zhengli, from the Wuhan Institute of Virology (WIV), of genomes of several bat SARS-related coronaviruses from the same mine in Yunnan province that RaTG13 (closest to SARS-CoV-2) came from. 8/
biorxiv.org/content/10.110…

I had thought it a bit suspicious that Dr. Shi's group had not published these genomes...

But then they did, and the genomes turned out to be less close to SARS-CoV-2 than RaTG13 (sampled in a bat in same mine). A sideshow to the main event of uncovering the origin of SC2. 9/

Both the genomes and the fact that they were published were reassuring. 10/

MUCH more important was an almost miraculous paper by Xiao Xiao, Zhou Zhaomin and others that definitively documented sustained sales of illegal wildlife, including plausible intermediate hosts like raccoon dogs and civets, in 4 wet markets in Wuhan. 11/
nature.com/articles/s4159…

This was painstaking work, involving monthly visits to 17 wildlife vendors at 4 markets from 2017 - Nov 2019. And it caught Chinese authorities in an embarrassing lie (or less plausibly an enormous mistake) in the WHO report released just before Xiao et al was published...12/

WHO report: "Market authorities have confirmed that all reported live and frozen animals sold in the Huanan market were from farms that were legally licensed for breeding and quarantine, and that no illegal trade in wildlife has been found..." . 13/

https://twitter.com/ggronvall/status/1417588683264430088?s=20

Leaving aside that lie/mistake, such clear evidence that live, illegal wildlife was indeed sold at these Wuhan markets, including Huanan market to which so many early cases were linked, was a game-changer. 14/

The Huanan market did not become a focus of interest out of the blue. It became a focus because so many of the very earliest cases turned out to be linked to it. 15/

Xiao et al's paper powerfully connected the dots between the early outbreak in the market and the presence of potential intermediate hosts known to transmit SARS-CoV-2 efficiently (like raccoon dogs). 15/

So, the ingredients of a SARS-type outbreak are staring us in the face in this case. And although I still believe a lab accident origin is not impossible, it is not the case that both scenarios are equally likely. 16/

In a follow-up thread I will discuss my current thinking about the geographic pattern of early cases in Wuhan. 17/

But I'll end here by saying that we need to keep our eye on the ball - zoonotic origins. Nature - plus human activities like illegal wildlife sales - will continue to deliver fastballs. 18/18