According to this report by Public Health England (p.35):
whilst vaccination may reduce an individual’s overall risk of becoming infected, once they are infected there is limited difference in viral load (and Ct values) between those who are vaccinated and unvaccinated. Given they have similar Ct values, this suggests limited difference in infectiousness.
If this is true, how would vaccination help stop the virus? Logic would suggest just the opposite: since vaccination does not decrease significantly infectiousness, chances for new (possibly deadlier) mutations to arise should increase. Could someone explain which piece of data I'm missing?