New work via @jepekar et al in @ScienceMagazine shows that there may have been two zoonotic leaps of SARS2 to humans in late 2019. science.org/doi/10.1126/sc… 1/
SARS2 genomic diversity before Feb 2020 likely comprised two distinct viral lineages (A & B), probably a result of two separate transmissions to humans. The first likely involved lineage B around 18 Nov 2019 (23 Oct–8 Dec), and the second (of A) likely occurred soon after. 2/
In early work on the origins of the pandemic that we published in @Nature in April of 2020, we used phone data to track human movements through Wuhan and showed how the virus initially spread through China. nature.com/articles/s4158… 3/
In subsequent analyses using these same data but going *backwards* rather than forwards (described in the afterword to the paperback version of #ApollosArrow -- amazon.com/Apollos-Arrow-…) we traced when SARS2 might have *arisen*. 4/
We use the same data and similar methods to reason backwards, not just forwards, and thus to estimate the date the first SARS2 infected patient left Wuhan and went elsewhere in China.
We call this patient 0’.
(Patient 0 is the unknown first patient who got infected.) 5/
We call this patient 0’.
(Patient 0 is the unknown first patient who got infected.) 5/
Our estimated date for the earliest such person 0' who left Wuhan and went elsewhere in China is Nov 1, 2019 (and the range is Oct 20 to Nov 13, 2019). This analysis based on phone data thus corresponds with this later genomic work based on the mutations in early variants. 6/
This means, given the known early epidemiology of SARS2, that the first patient to get infected (eg, from an animal via a zoonotic leap), likely did so in the middle of October 2019, and then gave the infection to 0' who migrated out (unless that first person also left Wuhan). 7/
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