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

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.

Differences in Clinical Presentation of COVID-19 in Children Hospitalized During Domination of Early (BA.1, BA.2) and Late (BA.5, BA.2.75, BQ.1 and XBB.1.5) SARS-CoV-2 Omicron Subvariants

“…21 In addition, infection with Omicron BA.1 and BA.2 subvariants was associated with more frequent upper respiratory symptoms and neurological complications. 6,8,21 Similar observations were made by authors from South Korea, who documented a higher proportion of patients with fever (89.9%), febrile seizures (8.8%) and croup (13.4%). 9 In our cohort, fever was significantly more frequent during LO period (87% compared to 79% during EO), but the prevalence of febrile seizures was low and did not differ according to the analyzed periods (1.5% during LO, and 0.87% during EO).…”

“…6 The authors concluded that the emergence of BA.5 had a more severe impact on children, as the incidence of hospitalizations and neurological complications (including febrile seizures with prevalence of 27.9% vs. 7.0% during BA.1/BA.2) increased significantly. 6 Thus, despite the overall good prognosis for children suffering from COVID-19 during LO, it should be considered that the impact of the new Omicron subvariants on pediatric patients seems to be different than in adults, in which better clinical outcomes were observed according to the data from SARSTer database. 25 In addition, selected cases, in particular older children with comorbidities and with confirmed radiological pulmonary lesions in the course of SARS-CoV-2 infection, should be managed with precaution.…”

“…10,12 Based on our observations, predictors of severe course of COVID-19 in children in terms of the currently dominating Omicron One Japanese study compared the clinical characteristics of children infected with SARS-CoV-2 Omicron variant BA.5 (July-August 2022) and BA.1/BA.2 (January-June 2022) in 13 hospitals. 6 The authors concluded that the emergence of BA.5 had a more severe impact on children, as the incidence of hospitalizations and neurological complications (including febrile seizures with prevalence of 27.9% vs. 7.0% during BA.1/BA.2) increased significantly. 6 Thus, despite the overall good prognosis for children suffering from COVID-19 during LO, it should be considered that the impact of the new Omicron subvariants on pediatric patients seems to be different than in adults, in which better clinical outcomes were observed according to the data from SARSTer database.…”

“…4,5 There are only scarce data in children analyzing the clinical course of COVID-19 during the Omicron domination and they mainly describe the first months of the Omicron occurrence. [6][7][8][9][10][11][12] Predictors of severe COVID-19 caused by currently dominating variants need to be established in pediatric patients. Thus, the aim of this study was to analyze the clinical course and severity of COVID-19 in children during the dominance of early and later Omicron subvariants to identify predictors of severe course of the disease in the pediatric population.…”

Factors affecting guardians' decision‐making regarding the SARS‐CoV‐2 vaccine

“…17 However, regarding the efficacy of vaccines and associated adverse reactions in children, the Japan Pediatric Society had to make recommendations based on overseas data alone 4 because the Japanese data were insufficient at that time. Since then, Japanese data have been accumulated, [18][19][20] but it has not yet been explained by the government to citizens in an easy-to-understand manner. Such accurate data are exactly what Japanese guardians desire to receive.…”