Thread by @kakape

Press conference on what @WHO-convened mission to investigate the origins of #SARSCoV2 found on their China trip is about to start in Wuhan.
(Was originally supposed to start an hour ago before being pushed back)

@WHO It finally started this minute.

@WHO After a lengthy introduction of the mission and its terms of reference, Liang Wannian, who leads the Chinese team of the joint mission, says he will now begin to talk about the key findings, starting with molecular epidemiology.

@WHO Wannian still running through a lot of background that we all know: Similarity of viruses found in bats and pangolins, susceptibility of cats, genomes linked to Wuhan market being identical to each other...

@WHO Sequence data "also showed that some diversity of viruses was already present in the early phase of the pandemic in Wuhan, suggesting unsampled chains of transmission beyond the Huanan market cluster”, says Wannian.

@WHO ILI data from a hospital in Wuhan and SARI surveillance data from a hospital in Hubei province was reviewed, says Wannian. "The findings indicated that there was no substantial unrecognized circulation of #SARScov2 in Wuhan during the latter part of 2019."

@WHO Wannian runs through other evidence and concludes this part:
"This is our basic judgment: It is not possible on the basis of the current information to determine how #SARSCoV2 was introduced into the Huanan market."

@WHO One key goal was to understand what happened in early December 2019, says @Peterfoodsafety.
"Did we did we change dramatically the picture we had beforehand? I don't think so.
Did we improve our understanding? Did we add details to that story. Absolutely."

@WHO @Peterfoodsafety Team did a “detailed and profound search” for cases that might have been missed, says @Peterfoodsafety. “We did not find evidence of large outbreaks that could be related to cases of #COVID19 prior to December 19 in Wuhan or elsewhere."

@WHO @Peterfoodsafety Picture becoming clearer of Huanan market being just part of the spread of #sarscov2 in Wuhan in December, says @Peterfoodsafety. “It was not just only a cluster outbreak in the Huanan market, but the virus was also circulating outside of the market."

@WHO @Peterfoodsafety It "is a very classical picture of the start of an emerging outbreak, where we start with a few sporadic cases early on in the month of December and then we start to see small outbreaks where the disease starts to spread in clusters” incl. the Huanan market, says @Peterfoodsafety

@WHO @Peterfoodsafety "All the work that has been done on the virus, and trying to identify its origin continue to point towards a natural reservoir of this virus and similar viruses in bat populations”, says @Peterfoodsafety. “But … a direct jump from bats in the city of Wuhan is not very likely."

@WHO @Peterfoodsafety Team evaluated four hypotheses, says @Peterfoodsafety. “We sat down and went through these different hypotheses, one by one, and assessed the likelihood by putting forwards arguments for and arguments against such hypotheses. And then assessing the likelihood of each of them."

@WHO @Peterfoodsafety The 4 hypotheses:
1. direct zoonotic spillover
2. spillover from an intermediary host species that might have allowed virus to adapt more
3. introduction via food chain, for example from frozen products
4. lab-related incident

@WHO @Peterfoodsafety "Our initial findings suggest that the introduction through an intermediary host species is the most likely pathway”, says @Peterfoodsafety. But direct spillover and food chain also need some more investigation.

@WHO @Peterfoodsafety “However, the findings suggest that the laboratory incident hypothesis is extremely unlikely to explain introduction of the virus into the human population”, says @Peterfoodsafety suggests the team will not further follow-up that hypothesis with more studies.

@WHO @Peterfoodsafety Still important to "try to identify earlier cases” to better understand early events, says @Peterfoodsafety. “We would recommend to continue some of the good work that has been initiated in looking for material that can be analyzed, that is still available from that time."

@WHO @Peterfoodsafety “A lot of this material has been already looked at”, says @Peterfoodsafety, but there are more sources left to analyse. "One of them just to give an example is blood samples from blood banks, and not only here in Wuhan and other cities and provinces”, but also in other countries.

@WHO @Peterfoodsafety “We need to conduct more surveys into certain animal species that could be the reservoir or act as a reservoir and of course, including more sampling and more studies of bat populations, not only in China”, says @Peterfoodsafety.

@WHO @Peterfoodsafety More work also needs to be done to understand "the possible role of the cold chain, frozen products in the introduction of the virus over a distance”, says @Peterfoodsafety.

@WHO @Peterfoodsafety "We know that the virus can persist and survive in conditions that are found in these cold and frozen environments”, says @Peterfoodsafety. "But we don't really understand if the virus can then transmit to humans and under which conditions this could happen"

@WHO @Peterfoodsafety #sarscov2 could "have taken a very long, and convoluted path involving also movements across borders, travels etc before arriving in the Huanan market”, says @Peterfoodsafety. “Therefore, it's also very interesting to follow up on every one of these clues” from other places.

@WHO @Peterfoodsafety Q about exact likelihood of different hypotheses.
Only "broad categories: most likely, less likely”, says @MarionKoopmans. May change with new data. "We can take this again and say okay with this new information does our assessment of the different pathways change?"

@WHO @Peterfoodsafety @MarionKoopmans Q: why did you discard the lab hypothesis?
Detailed evaluation in the report, says @Peterfoodsafety. Accidents happen, but are rare, he says. Also “the fact that nowhere previously was this particular virus researched or identified, or known”.

@WHO @Peterfoodsafety @MarionKoopmans Team also looked at the BSL4 lab in Wuhan Institute of Virology and "it was very unlikely that anything could escape from such a place”, says @Peterfoodsafety.

https://twitter.com/theakfischer/status/1359100732465573891

During visit of Wuhan Institute of Virology, team had a "very long, frank, open discussion with the management and the staff of the Institute“, says @Peterfoodsafety. They gave a "very detailed description of their research, both present and past." Minutes will be in report.

@Peterfoodsafety Well, this was a very long press conference considering there was not all that much news. The big take-away is that the origins mission has concluded that lab origin is “extremely unlikely” and that an intermediate host is the most likely scenario.

@Peterfoodsafety The most interesting clue was what @MarionKoopmans explained:
That some animals known (rabbits) or suspected (ferret-badgers, bamboo rats) to be susceptible to #SARSCov2 were at Huanan market and came from farms/traders in regions where bats are known to harbor related viruses.