Vagus, sorry for the delay but I was summoned to a unscheduled meeting.
OK, the thinking is that preventing symptomatic disease via vaccination will reduce the duration and level of infection in the community as a whole. This in turn would lead to a reduction in transmission. So by stopping infection, we should be stopping transmission.
There are issues with this all the same. If you've been vaccinated, the idea is that you don't get the infection anyway. However, if you are asymptomatic, you could still infect someone else.
For obvious reasons, Covid-19 transmission research has not been at the forefront of the minds of the scientists. Apart from anything else, it's very invasive, requires twice weekly swabbing and requires exposing people to the virus. This is why we need to appreciate that the battle has not been won over this devastating virus by vaccine development. Research is needed for many years to come.