Changing Trends of Respiratory Viruses in Hospitalized Children During and After the COVID-19 Emergency Phase in Yongin, South Korea (2020–22 vs. 2023–24)

The COVID-19 pandemic and subsequent non-pharmaceutical interventions (NPIs) significantly disrupted the epidemiology of pediatric respiratory viruses. This study compared infection patterns among 3658 hospitalized children in South Korea during the pandemic (2020-2022) and the post-emergency phase (2023-2024), following the relaxation of mandatory NPIs. Of 4419 eligible tests, the most frequently detected viruses overall were rhinovirus/enterovirus (HRV/HEV) (27.9%), influenza (14.5%), and respiratory syncytial virus (RSV, 11.9%). The post-emergency phase was marked by a dramatic surge in influenza virus (IFV), which surged dramatically (5.5% → 28.2%), and a more than two-fold increase in adenovirus (ADV) (5.7% → 12.5%) (<i>p</i> < 0.001). (<i>p</i> < 0.001). Conversely, parainfluenza virus (PIV) detection rates declined significantly (15.4% → 11.3%, <i>p</i> < 0.001). Demographically, post-emergency phase patients were significantly older (mean 4.9 vs. 3.5 years) and experienced a shorter hospital stays (3.2 vs. 4.3 days) (<i>p</i> < 0.001). Crucially, age-specific susceptibility shifts were evident. IFV rebounded across all pediatric ages but spiked severely in school-aged children and adolescents, while HRV/HEV demonstrated a clear proportional shift towards older age groups. These results demonstrate a substantial reconfiguration of the pediatric respiratory landscape, necessitating age-stratified surveillance and flexible public health strategies to mitigate the future infectious disease burden.