A single dose of the COVID-19 vaccine by either Pfizer or AstraZeneca brings downthe risk of a person transmitting SARS-CoV2 to their closest contacts by half. The conclusion is based on an analysis of over 3,65,000 households in the United Kingdom. The researchers found that the people who have been vaccinated for at least 21 days could still test positive for the virus. However, the viral transmission from these individuals to others in their households wasreduced by 40-50%,in which the first person to test positive had not been vaccinated. 

Resource: Internet resource. Nature. One vaccine dose can nearly halve transmission risk. April 30, 2021. Accessed on May 3, 2021,2021. Available from:

https://www.nature.com/articles/d41586-020-00502-w