https://www.scientificamerican.com/article/covid-variants-ma...
https://www.scientificamerican.com/article/covid-variants-ma...
The paper you cite supports this: in a case study of a single immunocompromised patient who---because of that---had a prolonged infection, many replications of the virus were observed. This patient represents a "hot spot" of variant emergence in this furthermore antibody treated patients. From the article "the remaining samples [sic: most] are consistent with arising from a consistent viral population".
What I take from this is: we ought to prevent prolonged infections where it is possible. Again, from the article "The effects of convalescent plasma on virus evolution found here are unlikely to apply in immunocompetent hosts in whom viral diversity is likely to be lower owing to better immune control." And a vaccinated individual will on average have the best immune control.
https://www.sciencedirect.com/science/article/pii/S026240792...
e.g. https://www.channelnewsasia.com/commentary/covid-omicron-var...
>Do the unvaccinated populations fuel the emergence of SARS-CoV-2 variants?
> The consensus among the scientific community is yes, they likely do. Unvaccinated people have less protection from the SARS-CoV-2 virus and thus would allow more of the virus to multiply within them.
> The higher rate of virus multiplication in the unvaccinated is likely to result in more possible mutations of the virus, resulting in the emergence of a larger number of variants in unvaccinated than vaccinated people.
I think at this point there is not much more to say here, at least from my end. Have a great day.