This study monitored 1898 health care workers after receiving full vaccination with the BNT162b2 mRNA vaccine. In a four-month period, only 10 workers tested positive for SARS-CoV-2, with a very low cumulative incidence (0.005%). The infections were mostly mild (60% of cases) or completely asymptomatic (40%). The study also compared the effectiveness of nasopharyngeal swabs and saliva samples in detecting the virus, finding that saliva is a viable alternative for surveillance. The results confirm the high efficacy of the vaccine, but underscore the importance of continued monitoring to identify asymptomatic carriers.