BACKGROUND: Patients with cancer are at high risk of severe or lethal COVID-19. The impact of SARS-COV-2 vaccination on the risk of developing COVID-19 was investigated in an exhaustive series of patients from a comprehensive cancer center. METHODS: This is a study of the exhaustive population of 2391 cancer patients who were prescribed SARS-COV-2 vaccination until 09/21. Patient characteristics, documented SARS-COV-2 infection with RT-PCR, and survival were collected. The primary endpoint was the rate of COVID-19 after vaccination. Secondary endpoints included risk factors to develop COVID-19 after vaccination, with a comparison with the cohort of vaccinated health care workers (HCW), and risk factors for death. RESULTS: From January to September 2021, among 2391 patients with cancer under active treatment in whom a SARS-COV-2 vaccine was prescribed, 659 (28%), 1498 (63%) and 139 (6%) received 1, 2, and 3 doses, respectively. Ninety five patients received a single dose of vaccine after a previous COVID-19. Two thousand two hundred eighty five health care workers (HCW) received one (N = 17, 0.7%), 2-3 (N = 2026, 88.7%) vaccine doses and one dose after COVID-19 (N = 242, 10.6%). With a median follow-up of 142 and 199 days for patients and HCW, respectively. Thirty nine (1.6%) patients and 35 (1.5%) HCW developed COVID-19 after vaccination. Six of 39 cancer patients and no HCW died because ofCOVID-19 within 50 days after diagnosis. Independent risk factors for COVID-19 in vaccinated patients were age, single dose of vaccine without previous COVID-19 and anti-CD20 treatment in the last three months. Independent risk factors for death included metastatic disease, gender, cancer type, but also documented COVID-19 before vaccination. CONCLUSIONS: Patients receiving two or more doses of COVID-19 vaccine have reduced risk of COVID-19. The risk of death of vaccinated cancer patients presenting COVID-19 remains high. COVID-19 before vaccination is associated with an increased overall risk of death.