In-Hospital Complications of Influenza A and B Among Hospitalized Australian Children in the Post-COVID Era

Influenza is a leading cause of pediatric hospitalizations, with clinical presentations and outcomes varying between types A and B. This study compared the clinical characteristics and complications of children hospitalized with influenza A and B at the Sydney Children's Hospitals Network (SCHN) in the post-COVID era.

We conducted a retrospective cohort study of children < 18 years admitted to SCHN with influenza during 2022-2023. Data on patient demographics, clinical presentations, complications, and management were extracted from electronic medical records. Group comparisons used chi-square or Fisher's exact tests, and modified Poisson regression estimated adjusted risk ratios (RRs) with 95% confidence intervals (CIs) for key clinical outcomes.

Among 704 influenza hospitalizations, 480 (68.2%) were due to influenza A and 224 (31.8%) to influenza B. Influenza B hospitalizations were more frequent in older children aged 5-< 18 years (67.4% vs. 57.7%) and associated with myalgia and pharyngitis, whereas influenza A hospitalizations were more common in children < 5 years (42.3% vs. 32.6%) and linked to cough, wheeze, and seizures. Although less common, influenza B hospitalizations exhibited greater clinical severity, with higher risks of noninvasive respiratory support (RR = 2.94; 95% CI 1.49-5.81) and intensive care unit (ICU) admission and/or mechanical ventilation (RR = 3.23; 95% CI 1.43-7.32).

Influenza B, though less prevalent, was associated with greater severity, particularly in older children. These findings underscore the importance of continued protection against both influenza types and support consideration of expanding vaccine access to children aged 5 years and older.