The more complex an organism, the more a proof-reading mechanism is required. Enveloped Coronaviruses are complex enough that a break of the proof-reading mech

The more complex an organism, the more a proof-reading mechanism is required. Enveloped Coronaviruses are complex enough that a break of the proof-reading mechanism will almost certainly also be fatal to the virus. That is why you're much more likely to see mutations in smaller simpler viruses like Rhinovirus - and why vaccination efforts are futile. ...but you are correct that this is a statistics question - at what number of infected humans, does the odds of a meaningful mutation occur? 10^6 humans? 10^9 humans? 10^12 humans? We don't really know.