Short- and Long-term Outcomes of children hospitalized with COVID-19 or Influenza: results of the AUTCOV study

Background: Recent literature gives different results on morbidity and mortality after COVID-19 as compared to Influenza hospitalized children and results of large, population based studies are scant. In this population-based study in Austria, we evaluated and compared the short- and long-term outcomes after COVID-19 or Influenza hospitalization and associations with their baseline drug profile. Methods: Individual data were provided on children ≤ 18 years hospitalized with COVID-19 in the years 2020 and 2021 or Influenza in 2016 to 2021 as well as on age-, sex- and region-matched controls from the Austrian Health Insurance Funds. The primary outcome was time to hospital discharge. Secondary outcomes were in-hospital death, all-cause mortality and readmission to hospital due to any reason. The median follow-up time was 430 days (IQR: 245-552) in the COVID-19 and 1221 days (IQR: 881-1599) in the Influenza group. Results: 1063 children were hospitalized due to COVID-19 and 2781 children due to Influenza in the study period. Children hospitalized due to COVID-19 or Influenza were more likely to have a larger disease burden as compared to the general population. Influenza hospitalized patients were observed to be generally younger and a larger percentage of polypharmacy than those with COVID-19. No significant difference in the time to hospital discharge was found between cohorts (HR: 1.22 [95%-CI: 0.97-1.55], p=0.093). The risk for readmission was significantly higher for Influenza (HR: 1.23 [95%-CI: 1.03-1.47], p=0.021). In-hospital mortality (0.94% vs. 0.22%, p=0.004) and long-term mortality (p=0.009) was significantly larger in COVID-19 patients. One-year mortality after hospitalization was estimated with 1.13% (CI: 0.49-1.77) in the COVID and 0.32% (CI: 0.11-0.53) in the Influenza group. Conclusion: A general picture of COVID-19 being a milder disease compared to Influenza may not be drawn. No significant difference for time to hospital discharge was observed between cohorts but the risk of readmission was significantly larger in the Influenza group. Death rates of COVID-19 hospitalized children seem to be higher, however, the low number of severe events may limit the findings.