Abstract Background The COVID-19 pandemic disrupted the circulation of common pediatric respiratory viruses worldwide. We assessed how virus-specific patterns among hospitalized children in South Korea changed between the pandemic and post-pandemic periods. Methods We retrospectively analyzed nasopharyngeal specimens from children under 18 years old admitted with acute respiratory symptoms to Yongin Severance Hospital from March 2020 to December 2024. Respiratory pathogens were detected using multiplex RT-PCR and FilmArray® panels; positives for influenza rapid antigen tests were included. Virus activity and age distributions were compared between the pandemic period (2020-2022) and the post-pandemic period (2023-2024). Results Of 5,173 tests, 4,419 (3,658 children) met inclusion criteria. The most frequently detected viruses overall were HRV/HEV (27.9%), influenza (14.5%), and RSV (11.9). Single-virus infections predominated, but 716 co-infections occurred; the most common dual combination was HRV/HEV + RSV (17.0% of co-infections). Detection patterns reflected a sharp early-pandemic suppression followed by a rebound. Compared with the pandemic period, children in 2023-2024 were older (mean 4.9 ± 5.0 vs. 3.5 ± 4.1 years; p 0.001) and had shorter hospital stays (3.2 ± 2.6 vs. 4.3 ± 2.7 days; p 0.001). Virus-specific shifts included: IFV A/B increased from 5.5% to 28.2% (p 0.001) and ADV from 5.7% to 12.5% (p 0.001), while HRV/HEV decreased from 36.9% to 30.9% (p = 0.001) and PIV 1-4 from 15.4% to 11.3% (p 0.001); RSV A/B remained similar (15.1% vs. 13.7%; p = 0.217). Age-virus distributions also shifted: post-pandemic HRV/HEV infections skewed toward older children; ADV rose markedly in toddlers and pre-schoolers (to 18.2% and 18.5% of detections, respectively); influenza surged across all ages, most prominently among school-aged children (54.5%) and adolescents (69.3%). RSV re-emerged with a broader age range and off-season surges before returning to a winter-dominant pattern by 2023-2024. Conclusions Pediatric respiratory virus epidemiology in South Korea underwent substantial, virus-specific reconfiguration during and after COVID-19. The pronounced rebound of influenza and adenovirus, age shifts in HRV/HEV and RSV, and sustained co-infections underscore evolving population immunity and the downstream effects of non-pharmaceutical interventions. Ongoing surveillance that integrates age strata and test-platform nuances is essential to guide vaccination timing, clinical preparedness, and resource allocation. This abstract is funded by: a faculty research grant of Yonsei University College of Medicine (6-2024-0099), and a new faculty research seed money grant from the Yonsei University College of Medicine for 2025 (2025-32-0027).
Kim et al. (Fri,) studied this question.