Yes, you need to wear a mask. At this stage, it is still unclear whether the current vaccine will also prevent the transmission of the virus to people around you. It is similar to the current situation where people have COVID-19 but suffer no symptoms. However, they are still able to transmit it to others. It may be only until a good majority of people have been vaccinated that restrictions to our daily lives are lifted.
For flu, experts say the herd immunity should be achieved when around 70% of the population gets vaccinated, so that is the current working theory for COVID-19. Read more