Outcomes of elderly hospitalized patients with influenza after the COVID-19 pandemic: decline of functional independence and frailty

Background Influenza remains a heavy burden to the elderly and the situation has been affected by the COVID-19 pandemic. The objective of this study was to clarify outcomes of elderly hospitalized patients with influenza after the COVID-19 pandemic. Methods The clinical data of patients 65 years of age or older who were severely ill with influenza and required hospitalization in one center were gathered between September 2023 and March 2026 (3 influenza seasons after the COVID-19 pandemic). The outcomes, functional independence, and frailty of them were analyzed. Results A total of 210 elderly patients were enrolled. The median age was 79 and 32 cases were judged as having mild or more frailty by the clinical frailty scale (CFS) before admission. Pneumonia was the most common disease indicated as cause for hospitalization, followed by a poor general condition and heart failure. The median duration of hospitalization was 13 days and in-hospital deaths were recorded for 17 patients (8.1%). Sixty cases changed hospital due to further treatment or deterioration of activity of daily living, and the functional independence measure (FIM) of 37 cases (17.6%) remained under a score of 70 even after rehabilitation. The CFSs worsened in 19 cases (9.0%) at the time of discharge. Conclusions Influenza infection remains a heavy burden among the elderly after the COVID-19 pandemic. The elderly tend to lose functional independence and fail to frailty even after recovery from acute illness. Preventive measures for influenza to avoid admission, including vaccination, will be essential. (Influenza Internet Survey, UMIN000015989)