It is a virtual certainty that a 4% likely event would occur given the millions of people that have been infected (and the subsequent mutations occurring within each of them). But that doesn't have anything to do with omicron specifically... and I certainly don't intend to suggest a correlation between NS/S and infectiousness. Mutations have a certain rate, but the events themselves are random.

I guess a different way to say this is -- It makes no sense to use the NS/S ratio as a rationale to claim that omicron was a lab-leak. The 33/4 ratio should be rare, but not unexpected. If you were going to claim that, the absolute increase in mutations would be a more compelling argument, but again, there are plausible reasons for how that could occur in the wild too.

We have very incomplete sampling data, so looking at a single strain and determining risk, or likelihood, is very difficult.