[NLips]

To get the 1% figure you have to include an unstated assumption, which is that a novel virus is just as likely to emerge from this lab as from all top 100 cities put together.

If we try to make a rough calculation from an unknowledgeable starting position, it might be more reasonable to say "just as likely to come from each 1M+ city as to come from each lab [of which there is one]". Then, if we didn't know the geographic origin, the lab probability is ~1% ( = 1/(100 cities + 1 lab)), but knowing the geographic start point you'd get 50%

P(this lab given Wuhan) = P(Wuhan given this lab) * P(lab) / P(Wuhan)

P(this lab given Wuhan) = 1 [this lab is in Wuhan!] * (1/101) / (2/101)

[himinlomax]

Fact is, there's nothing that points to Wuhan as being a more likely source of viruses in the first place. It's not a tropical rainforest area, for instance. And indeed, the closest wild relatives we know of have been found much farther south.

[NLips]

I agree? In the above I'm assuming equal likelihood between each lab and each city, rather than equally likely to have come from any lab vs any city. The second is a poor starting point as it suggests having two, 100, or 1M labs would mean no increased chance of coming from a lab vs 1 lab. That's why I suggest the first.