Comparison Of Disease Severity and Outcome in Vaccinated and Non-Vaccinated COVID-19 Patients: A Prospective Observational Study

Background: COVID-19 vaccination has emerged as a critical intervention to reduce disease severity and improve clinical outcomes. However, comprehensive data comparing clinical characteristics, laboratory parameters, and outcomes between vaccinated and non-vaccinated hospitalized COVID-19 patients remain limited. Methods: This prospective observational study was conducted at BMCRI-affiliated hospitals from April to July 2021. A total of 978 adult patients eligible for COVID-19 vaccination with confirmed SARS-CoV-2 infection were enrolled. Patients were categorized into vaccinated (partially or fully) and non-vaccinated groups. Demographics, clinical symptoms, comorbidities, laboratory parameters, radiological findings, and outcomes were analyzed. Results: Of 978 patients, 412 (42.1%) were vaccinated and 566 (57.9%) were non-vaccinated. Vaccinated patients demonstrated significantly lower disease severity with mild disease in 68.2% versus 45.4% in non-vaccinated patients (p<0.001). Non-vaccinated patients had higher rates of severe disease (32.3% vs 18.4%, p<0.001) and required mechanical ventilation more frequently (22.6% vs 8.7%, p<0.001). In-hospital mortality was significantly lower in vaccinated patients (4.4% vs 18.7%, p<0.001). Vaccinated patients had lower inflammatory markers including CRP (45.2±28.4 vs 68.9±35.7 mg/L, p<0.001) and D-dimer levels (1.8±1.2 vs 2.9±2.1 μg/mL, p<0.001). Conclusion: COVID-19 vaccination significantly reduced disease severity, hospital mortality, and need for mechanical ventilation among hospitalized patients. These findings support the critical importance of vaccination programs in reducing adverse COVID-19 outcomes.