Publication date: Jan 21, 2025

The spread of the BA. 5 Omicron variant of severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) has increased the number of hospitalized children. However, the impact of the spread of new omicron subvariants in children remains poorly described. This prospective observational study evaluated the clinical characteristics of children hospitalized with coronavirus disease 2019 (COVID-19) in 13 hospitals in Niigata, Japan, during September 2022-February 2024. The data were divided and compared across 3 periods based on the dominant subvariants: BA. 5/BF. 5/BF. 7 period (September 2022-April 2023), XBB/EG. 5 period (May-December 2023) and BA. 2.86/JN. 1 periods (January-February 2024). In addition, the COVID-19 vaccination rates in hospitalized patients were compared with those in the general population. In total, 298 children with COVID-19 were hospitalized during the study period. The patients’ median ages were 4. 7 years during the BA. 5/BF. 5/BF. 7 period, 1. 2 years during the XBB/EG. 5 period and 2. 4 years during the BA. 2.86/JN. 1 period. The peak monthly number of admissions decreased over time, with 44, 32, 19 cases/mo during the BA. 5/BF. 5/BF. 7 period, the XBB/EG. 5 period and the BA. 2.86/JN. 1 period, respectively. Dehydration/oral intake failure (37. 2%, 111/298) and febrile seizures (16. 8%, 50/298) were the predominant reasons for hospitalization. The COVID-19 vaccination rates in hospitalized children 5-11 years of age (11. 1%) and 12-15 years of age (38. 9%) were significantly lower than those in the general population (41. 5% and 71. 0%). Although the clinical impact of the Omicron subvariants in children diminished over time, they continued to pose a risk. Continued efforts are needed to protect children from this evolving virus.

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