Vaccines help prevent transmission. They are not 100% effective - the effectiveness depends on the vaccine and variant and study but quite high. That's a long way of saying that they "don't prevent transmission"
In the UK's vaccine surveillance report released today it showed the rate of infection in vaccinated individuals ages 40-79 was significantly higher than unvaccinated.
The same report says that early results indicate that a single dose of the mRNA vaccines provides a 35-50% reduction in transmissions. Given that the second shot dramatically improves the results, we can assume that number will improve. Those are fuzzy numbers whoever, as it is difficult to measure. The prevention of infections is 55-70%
