Being ‘fully vaccinated’ doesn't mean that one is ‘immune to COVID-19’. Though the vaccines are potent, there's still a 5% chance that one could still become infected. That is to say, while vaccination confers complete protection from Covid-19-related hospitalization and death, it doesn’t entirely prevent everyone who’s vaccinated from catching the infection. Vaccine efficacy of 95% tells us that of 100 fully vaccinated people who are dosed with Covid, only 5 would experience symptoms.
https://health.clevelandclinic.org/can-vaccinated-people-transmit-covid-19-to-others/
