COVID-19 Versus Influenza Hospitalizations in Late 2025 in Poland: A Multicenter Retrospective Comparison

<b>Background/Objectives</b>: COVID-19 and influenza remain major causes of seasonal hospitalizations, with increasing overlap toward the end of the calendar year. Comparative data from this late-year period remain limited, especially for the Central European region. <b>Methods</b>: We retrospectively analyzed adult patients hospitalized with COVID-19 or influenza between September and December 2025 in nine infectious disease units in Poland. Demographic, clinical, and laboratory characteristics were compared, and independent predictors of in-hospital mortality were identified using multivariable logistic regression. <b>Results</b>: A total of 227 patients with COVID-19 and 87 with influenza were included. COVID-19 hospitalizations predominated in September-October, whereas influenza admissions increased sharply in December. COVID-19 patients were older and more frequently had cancer. Length of hospitalization, baseline oxygen saturation, inflammatory markers, and pneumonia rates were similar between groups. In-hospital mortality was significantly higher among COVID-19 patients (14% vs. 6%). Among patients who died from influenza, none received the latest seasonal vaccine; among patients who died from COVID-19, 84.4% did not receive an updated COVID-19 vaccine. After adjustment, COVID-19 was independently associated with a fourfold increased risk of death, along with hypoxemia and pneumonia. <b>Conclusions</b>: During the last quadrimester of 2025, COVID-19 caused more hospitalizations and higher in-hospital mortality than influenza in Poland. Though other studies have evidenced that COVID-19 severity decreased, it remains to cause a substantial healthcare burden. Our findings also suggest earlier COVID-19 vaccination in Poland (initiated preferentially before September) and enhanced healthcare preparedness during late-year periods of viral co-circulation.