Vaccination does not prevent spreading. It was never claimed it would stop the spread.
It was never claimed the vaccine would prevent a person from getting the virus, or spreading it.
Certain people have been inferring that vaccination would stop the spread, which is simply not true. People are being given the false impression by various sources that if vaccinated, they can't get sick, which just isn't true.
The only official claim is that vaccination could reduce severity if a person contracts the virus, that's it.
All they have claimed is that people would get less sick and there would be less hospitalizations and deaths.