COVID-19 vaccines have been in use for such a short time that we do not yet know how efficiently the vaccines prevent the transmission of the virus from one person to another. However, in viral diseases, a symptomless carrier spreads the virus to a lesser degree than a carrier with manifest symptoms. Since COVID-19 vaccines provide protection against the coronavirus disease and its symptoms, everybody taking the vaccine can protect not only themselves but probably also others.
Another aspect we do not yet know about is how long the protection given by the COVID-19 vaccine against the serious disease form lasts. This is also an aspect that we will gradually know about more over time.
The COVID-19 virus is constantly transforming, and therefore the efficacy of the vaccines against the new virus variants and infections is monitored continuously. We now know that the currently used COVID-19 vaccines provide fairly good protection against the new COVID-19 variants so far recognised, but the protective efficacy may by weaker against certain variants. Further research is necessary and is constantly being performed. Through such research, we learn more about the efficacy of the vaccines against the transformed viruses.