Short- and long-term outcomes following COVID-19 or Influenza hospitalization in adults: results of the AUTCOV study.

Introduction: Large-scale registry-based studies on patients hospitalized with COVID-19 as compared to Influenza are scant, yet they are needed to re-evaluate the pandemic and the characteristics of patients at risk of severe outcomes. Methods: In this registry-based study from Austria, we examined short- and long-term outcomes after hospital admission due to COVID-19 or Influenza, also focusing on outcomes conditional on hospital survival. Data were provided on adults hospitalized with COVID-19 in the years 2020 and 2021 or with Influenza in 2016-2021, as well as on matched controls from the Austrian population. Analyses were performed separately for the four age groups (19-40, 41-64, 65-74, and ≥75 years). Results: Hospitalized COVID-19 and Influenza patients had a larger medication load as compared to the general population. Across all investigated age groups, polypharmacy was more frequent in the Influenza group. The risk for all-cause death in the entire follow-up period and death during hospital stay was higher in the COVID-19 group as compared to the Influenza group for all age groups ≥41 years. Furthermore, the duration of hospitalization was longer in patients with COVID-19. Notably, readmission rates were higher in Influenza patients, and mortality of hospital survivors was increased in younger Influenza patients aged 41-64 compared to COVID. Conclusion: In the first 2 years of the pandemic, COVID-19 had devastating effects on a non-immunized population, mainly in older patients and in patients with pre-existing serious comorbidities, but the health consequences of Influenza should not be underestimated.