Coronavirus disease 2019 (COVID-19) and seasonal influenza represent major respiratory viral illnesses associated with substantial morbidity and mortality among critically ill patients requiring invasive mechanical ventilation. Despite overlapping clinical presentations, epidemiological evidence demonstrates significant differences in disease progression, respiratory failure severity, inflammatory responses, and mortality outcomes between these conditions. This review-based research article critically evaluates death risk patterns among intensive care unit (ICU) patients receiving mechanical ventilation for COVID-19 and influenza infections. The study synthesizes epidemiological findings from multicenter cohort studies, retrospective analyses, national surveillance datasets, and comparative observational investigations published between 2020 and 2024. Methodological emphasis was placed on population-based cohorts, ventilatory characteristics, comorbidity adjustment models, discharge bias assessment, and ICU mortality determinants. The analysis demonstrates that mechanically ventilated COVID-19 patients consistently exhibited higher mortality risk compared with influenza patients across multiple healthcare systems, although mortality differences narrowed during later pandemic waves. Several determinants including acute respiratory distress syndrome severity, racial disparities, comorbidity burden, treatment limitation practices, hospital resource strain, and ventilatory mechanics significantly influenced mortality outcomes. Additionally, coding frameworks such as the Clinical Classification Software Refined (CCSR) for ICD-10-CM diagnoses improved epidemiological stratification and risk adjustment in large administrative databases. The findings further indicate that ICU mortality measurement remains vulnerable to discharge bias, hospice utilization, and heterogeneity in healthcare infrastructure. While influenza-associated respiratory failure remains clinically severe, COVID-19 demonstrated greater systemic inflammatory injury and prolonged ventilator dependency during the early pandemic phases. This study contributes a comprehensive epidemiological interpretation of mortality risk patterns among ventilated ICU populations and highlights the importance of standardized mortality assessment frameworks, multicenter surveillance systems, and longitudinal critical care analyses for future pandemic preparedness.