Abstract Background COVID-19 has been a major public health concern globally, and risk factors have played a crucial role in determining the outcomes of the disease. With the introduction of vaccines, the impact of these risk factors could change and alter the course of the pandemic. Methods Ambispective observational study performed among hospital workers of a university hospital in Cali, Colombia. From March 6th, 2020, to February 28th, 2022. Risk factors were assessed with a self-reported survey. Using the aRR calculated for each of the five waves of COVID-19 in Colombia, mixed-effects models were constructed to obtain the association strengths in the pre- and post-vaccination era. Results A total of 480 patients, 71.8% were females. The median age was 32 years (27 - 39). In the pre vaccination era there were 169 (35.21%) COVID-19 cases and 165 cases (34.3%) in the post vaccination. In the pre-vaccination era, associated factors were being a healthcare worker (HCW) (aRR 2.12 (95%CI: 1.19-3.79)), technician (aRR 1.73 (1.26-2.38)), living with COVID-19 patients (aRR 2.10 (1.39-3.18)), immunosuppressive medication(aRR 3.88 (1.90-7.70)), self-perceived continuous exposure to COVID-19 patients (aRR 0.28 (0.21-0.37)), and a first COVID-19 episode during the first wave (aRR 0.05 (0.01-0.35)). In the post-vaccination era, COVID-19 history (aRR 0.49 (0.34-0.70)), vaccination in the past 6 months (aRR 0.13 (0.07-0.24)), positive anti-S antibodies in the last 3 months (aRR 0.55 (0.31-0.97)), and positive anti-N antibodies in the last 6 months (aRR 0.35 (0.17-0.74)) were associated. Figure 1. Risks factors for COVID-19 in pre and post vaccination era. In the pre-vaccination era, being a healthcare worker (HCW), technician, living with COVID-19 patients, immunosuppressive medication, self-perceived continuous exposure to COVID-19 patients and a first COVID-19 episode during the first wave were risk factors. while in the post-vaccination era, COVID-19 history, vaccination in the past 6 months positive anti-S antibodies in the last 3 months, and positive anti-N antibodies in the last 6 months were associated with COVID-19. Conclusion This study highlights the dynamic nature of risk factors after the introduction of vaccination. Educational level, being a healthcare worker, working in hospitalization areas, and living with COVID-19 patients were significant risk factors before vaccination. While increased positivity and S-antibody levels linked to vaccination were associated to lower risk of COVID-19 in the post-vaccination era. Disclosures All Authors: No reported disclosures