Comparison of Severe COVID-19 Outcomes in Vaccinated and Unvaccinated Patients, with and Without Diabetes Mellitus in a Romanian Tertiary Healthcare Pneumology Hospital—A Retrospective Study

The coronavirus disease 2019 (COVID-19) pandemic has had an unprecedented impact on public health. In the present study, we aimed to analyze the association of certain inflammatory biomarkers with severe COVID-19 and to explore the role of diabetes mellitus (DM) and vaccination status in relation to COVID-19 severity, intensive care need and mortality. Associated comorbidities (DM, obesity, cardiovascular, neurological, endocrine, hepatic, renal, pulmonary, rheumatological, psychiatric, hematological diseases, cancer and HIV), as well as inflammatory biomarkers, like ferritin, erythrocyte sedimentation rate (ESR), C-reactive protein (CRP), fibrinogen, lactate dehydrogenase (LDH), neutrophil-to-lymphocyte ratio (NLR), platelet-to-lymphocyte ratio (PLR), and systemic immune-inflammation index (SII) were analyzed in 866 subjects, according to vaccination status. In unvaccinated subjects, the highest AUROC curve for severe COVID-19 was recorded for CRP (0.668), and in the vaccinated group, the highest was recorded for SII (0.694). In age- and comorbidity-adjusted analyses, diabetes mellitus was associated with higher odds of severe COVID-19, ICU admission, and mortality among unvaccinated patients. This analysis was not feasible in the vaccinated group because of the very low number of unfavorable outcomes. These findings emphasize the potential role of vaccination in attenuating the excess risk linked to comorbidities-particularly diabetes mellitus-and support the use of accessible inflammatory biomarkers for early risk stratification. The results should be interpreted within the specific epidemiological phases of the pandemic and in the context of the observational study design.