People who are vaccinated against Covid-19 erroneously believe that they are completely safe, and that they can't ever transmit the virus. Both beliefs are incorrect.

Vaccinated people are less likely to catch Covid-19 when exposed, and less likely to transmit the virus if they are infected, but the probability is not zero. You still need to wear a mask to reduce those probabilities. You still need to keep distance from others.

These precautions can potentially drive R below 1 and make Covid-19 dwindle, if we keep doing all of them.