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. 2023 Jun 1;42(6):503-509.
doi: 10.1097/INF.0000000000003894. Epub 2023 Mar 2.

Comparison of Clinical Characteristics of Children Infected With Coronavirus Disease 2019 Between Omicron Variant BA.5 and BA.1/BA.2 in Japan

Tatsuki Ikuse  1 , Yuta Aizawa  1 , Takayuki Yamanaka  2 , Satoshi Hasegawa  3 , Takanori Hayashi  4 , Miyako Kon  4 , Tsutomu Tamura  4 , Akihiko Saitoh  1
Affiliations

Comparison of Clinical Characteristics of Children Infected With Coronavirus Disease 2019 Between Omicron Variant BA.5 and BA.1/BA.2 in Japan

Tatsuki Ikuse et al. Pediatr Infect Dis J. .

Abstract

Background: The emergence of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variants has dramatically altered the clinical profile of pediatric coronavirus disease 2019 (COVID-19). In Japan, we experienced a pandemic of omicron subvariant BA.1/BA.2 from January through June 2022. However, after the emergence of BA.5 in early July 2022, the number of children hospitalized with COVID-19 increased dramatically in Japan.

Methods: We collected data on monthly numbers of cases and clinical characteristics of hospitalized children with COVID-19 in 13 hospitals, the total number of pediatric COVID-19 cases, and COVID-19 vaccination rates in Niigata, Japan, for the period from January 2020 through August 2022. We compared clinical presentation during the periods of BA.1/BA.2 predominance (January-June 2022) and BA.5 predominance (July-August 2022) and estimated vaccine effectiveness (VE) against hospitalization during the BA.5-predominant period.

Results: Between January 1, 2020, and August 31, 2022, 49,387 children (19,085 children/100,000 population) were newly diagnosed as having COVID-19, and 393 were hospitalized for COVID-19. Hospitalization for febrile seizure, especially complex seizure, was significantly higher during BA.5 predominance than during BA.1/BA.2 predominance (27.9% vs. 7.0%, P < 0.01). VE against hospitalization during BA.5 predominance was estimated to be 75% (95% confidence interval, 48%-88%, P < 0.01).

Conclusions: The emergence of BA.5 significantly affected children in Japan; the number with complex febrile seizure who required hospitalization was higher than during BA.1/BA.2 predominance. The COVID-19 vaccination rate in children must be increased to prevent hospitalization for COVID-19 and to prepare for current and future variant outbreaks.

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Conflict of interest statement

The authors have no funding or conflicts of interest to disclose.

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