Acute COVID-19 in unvaccinated children without a history of previous infection during the delta and omicron periods

ABSTRACT

Background

The Omicron variant has been the predominant severe acute respiratory syndrome coronavirus 2 variant circulating in Korea since January 2022. This study evaluated and compared the clinical characteristics of children with coronavirus disease 2019 (COVID-19) between the Delta and Omicron periods.

Methods

The medical records of children aged < 12 years diagnosed with acute COVID-19 (<2 weeks of symptom onset) at seven university-affiliated hospitals were retrospectively reviewed. Children with a previous history of COVID-19 or vaccination were excluded. The clinical characteristics of the included children during the Delta (1 August 2021 to 15 January 2022) and Omicron (16 January to 30 June 2022) periods were compared.

Results

Among the 515 children included in the study, 36 (7.0%) and 479 (93.0%) were diagnosed with COVID-19 during the Delta and Omicron periods, respectively. A total of 142 (27.6%) were hospitalized, and the hospitalization rate was higher during the Delta period than the Omicron period (91.7% vs. 22.8%, p < 0.001). The incidence of fever (p = 0.009), vomiting (p = 0.031), and seizures (p = 0.007) was higher during the Omicron period, whereas the incidence of rhinorrhea (p = 0.027) was higher during the Delta period. Clinical severity and outcomes were comparable between the two periods. During the Omicron period, 6.4% of the hospitalized children received oxygen therapy and 1.8% received intensive care.

Conclusion

The incidence of fever and seizures was higher during the Omicron period in pediatric patients without a history of vaccination or previous COVID-19. However, the clinical severity was similar during both periods.

GRAPHICAL ABSTRACT

KEYWORDS:

• SARS-CoV-2
• COVID-19
• child
• clinical characteristics
• comparative study
• Omicron
• Delta
• Korea

Declaration of financial/other relationships

All authors have no conflicts of interest to declare.

Reviewer disclosures

Peer reviewers on this manuscript have no relevant financial or other relationships to disclose.

Author contributions

Conceptualization: HJY and HSB.

Data curation: KJM and HJY.

Formal analysis: KJM and HSB.

Methodology: HJY and HSB.

Software: KJM and HSB.

Validation: HJY and HSB.

Investigation: KJM and HJY.

Writing – original draft: HSB.

Writing – review & editing: KJM, HJY and HSB.

Acknowledgments

The authors gratefully thank Eu Gene Park, Hwan Soo Kim, Joo Young Lee, Yeji Kim, Yejin Kim and Young Hoon Kim for assistance with patients’ data collection.

Additional information

Funding

This paper was not funded.