the vast majority of viral replications take place in susceptible infected bodies, i.e. predominantly those of unvaccinated individuals. variants, therefore, mostly arise among unvaccinated. sometimes, by chance, a variant then may emerge that is able to evade some of the vaccine induced immunity. unvaccinated individuals therefore represent a source of escape variants, and therefore jeopardize the success of vaccine campaigns.
> the vast majority of viral replications take place in susceptible infected bodies, i.e. predominantly those of unvaccinated individuals.
I'm not sure this is true, but even if it is, this...
> variants, therefore, mostly arise among unvaccinated.
...does not follow from it. The key thing driving evolution of variants is not number of replications but selective pressure. Selective pressure is much larger in a vaccinated individual than an unvaccinated individual (or at least an unvaccinated individual that has not had COVID and does not have natural immunity).
Selection can drive evolution, and in a vaccinated body there exist other selection pressures than in an unvaccinated body. Variants which may by chance be suited well to strive in a new environment need to arise first. This will happen only when replication occurs. The unvaccinated population is the major breeding ground for variants, not the other way around.
