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Background: Ritonavir-boosted nirmatrelvir (N/r) is an antiviral which targets the main viral protease, administered to prevent the progression of SARS-CoV-2 infection in patients at high risk for severe COVID-19. We present a real-life case-control study evaluating the efficacy of N/r therapy in SARS-CoV-2 omicron variants positive outpatients in Campania region, Italy, with the aim of assessing the occurrence of three outcomes (hospital admission, admission in ICU and death) in cases and controls., Methods: We enrolled SARS-CoV-2 positive subjects that came to our attention in Early antiviral treatment ambulatory of Infectious Diseases ward of University Federico II of Naples, Italy from January 1st, 2022, to December 31st, 2022, during the first five days from symptoms occurrence. Patients were enrolled as cases or controls if they were treated with N/r or not treated at all, respectively., Results: 1064 patients were included (cases: 423, controls: 1184). Cases showed a lower mortality compared with controls while no differences were observed for other outcomes. Vaccinated patients showed a lower mortality compared with non-vaccinated ones (0.5% vs. 7.8%, p < 0.001). After full-matching propensity score, N/r reduced hospitalization rate only in unvaccinated patients. In contrast N/r significantly reduced mortality regardless of vaccination status., Conclusions: Treatment with N/r has proven effective in reducing mortality among outpatients with SARS-CoV-2 infection during several omicron variant surges. The beneficial effect of N/r treatment in reducing progression is more pronounced in unvaccinated patients., Competing Interests: Declarations. Ethical approval and consent to participate: This study was approved by the ethics committee “Comitato Etico Università Federico II-A.O.R.N. A.Cardarelli” (protocol number 0015191, 22nd March 2023). The informed consent was collected for all patients included in the study. The informed consent from control patients was obtained via telephone interview. This method of consent collection was thoroughly reviewed by the ethics committee, ensuring that it met all ethical standards. The informed consent from case patients was written. The records of the telephonic interviews conducted with control participants, included their verbal informed consent, are stored by the study’s data manager at the Department of Clinical Medicine and Surgery, University of Naples Federico II, Via Sergio Pansini 5, 80131, Naples, Italy. These can be retrieved and reviewed upon request by any relevant authority. Consent for publication: Not applicable. Competing interests: Prof. IVAN GENTILE reports personal fees from MSD, AbbVie, Gilead, Pfizer, GSK, SOBI, Nordic/Infecto Pharm, Angelini and Abbott, as well as departmental grants from Gilead and support for attending a meeting from Janssen, outside the submitted work.All other authors have no competing interests to declare., (© 2024. The Author(s).)