This is technically true.Every vaccinated person is a potential selection filter that can spin off a variant.
It does require that not only does the vaccine fail enough, but that they then have enough virus replication and go on to infect someone else (could be an unvaccinated person for the next step, doesn't matter). So, it's not a slam dunk going to happen, but it is a risk.
The only way to eliminate this risk is to minimize the virus and vaccinated person interactions. Keep the count low enough that it's unlikely.
There's not many ways to do that.
- We could not vaccinate anyone. No vaccine breakthrough variants then. No protection either.
- We could vaccinate enough people to drive community spread super low. This way there are relatively few virus vs vaccinated interactions.
- We could segregate the vaccinated from the unvaccinated. The vaccinated group will have low community spread. The vast majority of virus vs vaccinated interactions involve the other person being unvaccinated.
Unfortunately, we seem to be headed for the third option slowly.
As a vaccinated person, this is party of why I care about how many unvaccinated people there are. I would like to get to option 2 as fast as possible to minimize this risk. I'm not worried it's going to happen all at one time. Just slowly, one mutation that's more vaccine resistant and replicates faster than Delta at a time. Might just be a mutation that replicates fast enough that does it.