That means the vaccinated can get it from the vaccinated and it can mutate further.
The CDC has stated that vaccinated people can and do get infected, and spread the virus, but have a mild illness in general. Data shows this, including data from colleges like Cornell that report surveillance test data from their population of 95% vaccinated individuals.
That means that vaccinated people can spread the vaccine to each other, and the unvaccinated, and that the virus is busy mutating in their bodies too. From a mutation point of view the vaccinated hosts provide a selection pressure against virus mutations that the vaccine works well against.
That leads to the evolution of mutations which can evade the vaccine.
There really is no difference between the unvaccinated and the vaccinated except for the personal risk the unvaccinated are taking that they might have a severe case of COVID.
The plans from 2020 to actually eradicate COVID-19 are not realistic anymore since it has spread worldwide.