[taneq]

I don’t know if it counts as “rapid” given the infected population and time scale involved. Getting from the original COVID-19 to Delta+ in a lab would take a long time compared to in the millions of infected humans ‘in the wild’.

[sudosysgen]

It's a single nucleotide mutation. I don't see how the dozens of nucleotides from before would have been easy but the last nucleotide would be impossible.