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

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.

Household Secondary Transmission of the Severe Acute Respiratory Syndrome Coronavirus 2 Alpha Variant From a Community Cluster in a Nursery in Japan.

BACKGROUND: Spread of variants of concerns (VOCs) of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has led to an increase in children with coronavirus disease 2019 (COVID-19). In February 2021, clusters of the Alpha variant of SARS-CoV-2 started to be reported in Niigata, Japan, including a large nursery cluster. We investigated the transmission routes and household secondary attack rates (SARs) in this cluster. METHODS: Epidemiologic data related to a nursery cluster in Niigata, Japan, particularly child-origin and adult-origin SARs, were analyzed. VOCs were confirmed by whole-genome sequencing of virus from patients. RESULTS: In total, 42 persons (22 children and 20 adults) in the cluster were infected with the Alpha variant. In the nursery, 13 of 81 children (16.0%) and 4 of 24 teachers (16.7%) were infected. SARS-CoV-2 later spread to 25 persons (10 children and 15 adults) outside the nursery. Child-origin and adult-origin household SARs were 27.7% (13/47) and 47.0% (8/17) ( P = 0.11), respectively, which were higher than rates attributable to non-VOCs in previous studies. CONCLUSIONS: As compared with non-VOCs, the Alpha variant of SARS-CoV-2 exhibited high transmissibility among children and adults and may pose a high risk for household secondary transmission from SARS-CoV-2-infected children. Increased transmissibility of current or future VOCs could lead to greater transmission from children to adults or other children.

Changes in Exanthema Subitum Incidence and Patient Age Distribution During the COVID-19 Pandemic in Japan.

Incidences of community-acquired infectious diseases other than COVID-19 decreased during the coronavirus disease 2019 pandemic; however, exanthema subitum incidence before (2016-2019) and during the pandemic (2020) in Niigata, Japan, did not substantially differ, although the proportion of age less than 1-year-old was lower in 2020. These findings suggest that exanthema subitum is transmitted mainly among family members, not in the community.