Background: Paxlovid was granted emergency use authorization for the treatment of mild to moderate COVID-19, based on the interim analysis of EPIC-HR trial. Paxlovid effectiveness needs to be assessed in a noncontrolled setting. In this study we used population-based real world data to evaluate the effectiveness of Paxlovid. Methods: The database of the largest healthcare provider in Israel was used to identify all adults aged 18 years or older with first ever positive test for SARS-CoV-2 between January and February 2022, who were at high risk for severe COVID-19 and had no contraindications for Paxlovid use. Patients were included irrespective of their COVID-19 vaccination status. Cox hazard regression was used to estimate the 28 day HR for severe COVID-19 or mortality with Paxlovid examined as time-dependent variable. Results: Overall, 180,351 eligible were included, of them only 4,737 (2.6%) were treated with Paxlovid, and 135,482 (75.1%) had adequate COVID-19 vaccination status. Both Paxlovid and adequate COVID-19 vaccination status were associated with significant decrease in the rate of severe COVID-19 or mortality with adjusted HR 0.54 (95% CI, 0.39-0.75) and 0.20 (95% CI, 0.17-0.22), respectively. Paxlovid appears to be more effective in older patients, immunosuppressed patients, and patients with underlying neurological or cardiovascular disease (interaction p-value <0.05 for all). No significant interaction was detected between Paxlovid treatment and COVID-19 vaccination status. Conclusions: This study suggests that in the era of omicron and in real life setting Paxlovid is highly effective in reducing the risk of severe COVID-19 or mortality.