Association between the number of comorbidities and all-cause mortality during the COVID-19 pandemic: A Danish nationwide, retrospective cohort study.

Objectives: Chronic illnesses have been linked to elevated risks of hospitalization and mortality during the COVID 19 pandemic. While many studies have examined how specific comorbidities influence outcomes among hospitalized COVID 19 patients, less is known about how the pandemic affected all cause mortality among comorbid individuals in the general population. Our objective is to assess how the number of pre pandemic comorbidities interacted with COVID 19 and whether all cause mortality risks for individuals with comorbidities changed during the pandemic. Methods: This is a population-based retrospective cohort study, where we analyzed the entire Danish population aged 45 years and older using nationwide registry data. We examined COVID 19 specific and non COVID 19 mortality in 2020-2021 to capture both direct and indirect pandemic effects. Survival analysis techniques were applied to estimate mortality patterns across comorbidity levels. Results: Kaplan-Meier curves indicated that traditional comorbidity gradients persisted for non COVID mortality, whereas COVID 19 mortality showed a relative equalization across comorbidity groups. Gender and educational disparities remained evident. Conclusion: The findings highlight the need for preparedness strategies that protect medically vulnerable groups while addressing persistent social inequalities. They also demonstrate the importance of population wide approaches for understanding the full mortality impact of pandemics.