Thread by @mlipsitch

.@alisonannyoung has been one among the most active, persistent, and fair-minded reporters covering lab accidents in the US @USATODAY. This long piece makes the serious case for investigating poss lab origin for #SARSCoV2. usatoday.com/in-depth/opini….

This is not about conspiracy theories or China-bashing. This is about the basic principle, at least as old as Rev. Bayes and Sherlock Holmes, that when something unusual happens, you have to consider explanations that are also individually unlikely.

To be explicit, the @WHO mission's conclusion that a lab accident was unlikely was unjustified (as @alisonannyoung notes they are frequent) but even if true, global pandemics are also uncommon, so by definition the sequence of events leading to one do not happen all the time.

Many responses to this from various perspectives. I don't claim a lab accident is the most likely, only that it is a candidate among others with enough plausibility to need investigating.

Several responses including from @arambaut whose views on all such topics I hold in the highest regard emphasized the lack of evidence that the virus was ever in WIV.

If the @WHO mission report documents that 1) there is system at WIV such that no virus is handled in the lab without being sequenced; 2) no sequence plausibly ancestral to SARS-CoV-2 was recorded; and 3) the records examined were complete, then lab hypothesis wd be less likely.

Happy to be corrected but 1 is implausible because wild samples containing many viruses not explicitly studied were handled there and could have infected a worker subclinically. 2 seems true from my limited understanding. 3 seems not true from what I've read.

Note that in many western countries including the Netherlands cmr.asm.org/content/21/3/4… and the US journals.sagepub.com/doi/10.1177/15…, and the UK theguardian.com/science/2014/d…, lab accidents are not routinely made public and are shrouded in various levels of secrecy.

Asking if there may have been an accident in Wuhan is _not_ equivalent to asserting a conspiracy, among other reasons because a lab worker contaminated by a bat sample and asymptomatically transmitting to others is one possible scenario, in which case perhaps no one would know.

Again, not saying this or any other scenario happened, but that the WHO's public statements to date provide little reason to change one's priors one way or the other. That may be where we end up, as there may not be conclusive evidence.

But without citing more detailed evidence, WHO mission's conclusion means either they had a 0 prior on lab accident which is unaffected by evidence, or they have evidence they haven't yet made public, or they are overinterpreting the evidence they have made public.