Introduction: The control and prevention of SARS-COV-2 infection is based on both the respect of individual protection measures and distancing, but also on vaccination. This work aims to evaluate the impact of vaccination on SARS-CoV-2 infection among health professionals at CHUIR and to correlate with the positivity of screening tests. Methods: This is a retrospective study conducted over the period from 15 June 2021 to 1 September 2021. The diagnosis was based on RT-PCR defined and the antigenic test. The healthcare professionals were divided into 2 groups: G1-vaccinated / G2-non vaccinated. The comparison concerned the viral load in positive cases by means of the threshold values (Ct) of RT-PCR and the positivity of the antigenic test. Results: During the study period, 1658 healthcare workers were tested of which 638 were positive, representing a positivity rate of 39%. Clinical symptoms were present in 99% of all positive cases. G1: contains 440 health professionals representing 69% of all positive cases. G2: presents 198 positive non-vaccinated subjects, representing 31%. The average Cts in vaccinated and non-vaccinated subjects was n=24. Conclusion: Understanding the determinants of transmission, including human behavior and vaccine efficacy, is essential for the development of prevention strategies.