Differences between influenza and COVID-19 patients who required hospitalization: A study of the 2024-2025 season

During the winter and spring of 2024-2025, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) XEC subvariant became the main cause of the epidemic, and at the same time, major influenza epidemics were also observed. To clarify the differences between COVID-19 and influenza, we conducted a comparative study of patients who required hospitalization during the same period.

We compared 193 patients with COVID-19 Omicron XEC subvariant and 98 patients with influenza H1N1 pdm09 who required hospitalization.

The following characteristics were significantly more common in the COVID-19 group than in the influenza group: 1) males, 2) patients with chronic kidney disease, malignant tumors, autoimmune diseases, and patients using immunosuppressants, 3) patients with multiple underlying diseases, 4) healthcare-associated pneumonia, 5) pure viral pneumonia, 6) aspiration pneumonia, 7) cases in which antivirals had not been used since the diagnosis of infection, 8) patients who required invasive mechanical ventilation management or intensive care unit admission, and 9) deaths. On the other hand, the following characteristics were significantly more frequently observed in the influenza group than in the COVID-19 group: 1) patients without underlying diseases, 2) patients who had been vaccinated within the past year, 3) community-acquired pneumonia, and 4) mixed bacterial pneumonia.

There were many differences between the COVID-19 group and the influenza group that required hospitalization. The rates of severe illness and mortality in the elderly remain high in the COVID-19 group.