There’s some good evidence now from Public Health England and from the Oxford/AstraZeneca trials that the vaccines do prevent transmission.But they don’t completely prevent transmission. The figures are still being calculated but it’s in the order of 50%.
So, there will be some reduction in transmission, no doubt at all, but it’s still possible, even though you’ve been vaccinated, to get infected, have no symptoms and transmit it to others. That’s why it’s important that all those who get vaccinated still stick to the rules.