The results are preliminary as we wait for larger trials, but in what will likely hold for all vaccines, AstraZeneca reported today that their vaccine seems to have cut COVID-19 transmission by at least half (they determined this by continuing to collect nasal swabs and comparing PCR test results between those who received vaccine and those who did not). They intend to eventually also test people who were near the vaccinated, but that type of study will take much longer. But, it is expected that keeping people negative for COVID-19 will also prevent spread. So, here we find a vaccine that not only successfully prevents most symptomatic cases, but in fact prevents most cases altogether, which would greatly reduce spread.
AZ's efficacy also rose to 70% with more data and they claim they are finding even higher efficacy if they space out doses by 12 weeks.