Hospitalizations and In-Hospital Fatality Among Influenza Patients in the Pre-Pandemic and COVID-19 Pandemic Periods

Background/Objectives: Despite being a vaccine-preventable disease, influenza continues to pose a significant global health challenge, with clinical severity increasing at the extremes of age. This study aimed to describe influenza hospitalizations and hospital-related fatality rates in Poland in the pre-pandemic and COVID-19 periods. Methods: This retrospective population-based study included 39,604 hospital admissions with a diagnosis of influenza in Poland. Data were extracted from the National General Hospital Morbidity Study conducted by the National Institute of Public Health for the period 2016-2022. Results: Based on the hospital registry and data on the general population, an upward trend in hospitalization rates was observed in 2016-2020. In subsequent years, the lowest hospitalization rates were observed in 2021 and the highest ones in 2022, accounting for 1.3 and 30.3 hospitalizations per 100,000, respectively. Two hospitalization peaks were observed, one for children 0-5 and the other for adults 65-70 years of age. After the COVID-19 outbreak in Poland, an increased percentage of hospitalizations was observed in children and adolescents, and a decreased frequency was found in the elderly. The overall hospitalization fatality rate during the study period accounted for 2.9%, and the authors observed a decrease in the in-hospital fatality rate after the COVID-19 outbreak compared to the pre-pandemic period (3.4% vs. 2.1%, p < 0.001). Conclusions: This study highlights recent trends in influenza hospitalizations and in-hospital mortality before and during the COVID-19 pandemic in Poland, providing important data for optimizing prevention strategies and serving as a foundation for global comparative analyses.