Clinical and Economic Inpatient Burden of Influenza and Influenza-Like Illness in Germany 2019-2025: Analysis of Nationwide Hospital Data.

INTRODUCTION

Data on the influenza burden in Germany during and after the global COVID-19 pandemic are limited. This study presents nationwide trends in the clinical and economic inpatient burden of influenza and influenza-like illness (ILI) in the German population from 2019 to 2025.

METHODS

We conducted a descriptive, retrospective analysis of nationwide hospital data from the German Institute for Hospital Reimbursement covering six consecutive influenza seasons (2019-2020 to 2024-2025). Influenza/ILI hospitalizations were identified using the International Classification of Diseases version 10 (ICD-10) codes J09-J11 recorded as primary diagnosis. Outcomes included hospitalization counts, incidence rates, mean length of stay, ICU admissions, in-hospital mortality, and estimated costs, and were reported for three age groups (0-17 years, 18-59 years, ≥ 60 years). Regional variation across federal states was assessed using directly age-standardized rates.

RESULTS

We identified 240,646 influenza/ILI hospitalizations, with the highest burden observed in the 2024-2025 season (87,745 cases; incidence: 105.0/100,000 population). Less than 5000 cases were observed in both the 2020-2021 and 2021-2022 seasons. Across all seasons, adults aged ≥ 60 years accounted for 48% of hospitalizations and 92% of 10,054 in-hospital deaths. In this age group, in-hospital mortality ranged between 5.8% and 12.3% per season. Mean hospitalization costs per case increased during the study period and were highest in older adults, reaching €5430 in 2023-2024 and €5421 in 2024-2025. Total inpatient costs of influenza/ILI were highest in 2024-2025 and estimated at €390 million. Regional hospitalization rates varied considerably, but patterns were inconsistent across seasons.

CONCLUSIONS

Influenza/ILI causes a substantial and re-emergent inpatient burden in Germany, disproportionately affecting older adults. These findings highlight the need for sustained prevention efforts to reduce the burden of influenza/ILI in Germany. Further research is needed to understand the substantial regional disparities between federal states.