Coronavirus (COVID-19) Collection
High population burden of Omicron variant (B.1.1.529) is associated with the emergence of severe hepatitis of unknown etiology in children
The Omicron variant (B.1.1.529) emerged in late 2021, causing a widespread epidemic across the world, including in countries that had taken containment strategy with “zero-COVID” policy (Petersen et al., 2022). In industrialized countries that have experienced major extensive epidemics of Omicron, substantial fraction of the population was exposed, including children. For instance, a published seroepidemiological study in the United States indicated that approximately 75% of children have been infected by the end of February 2022 (Clarke et al., 2022).Transmissibility of asymptomatic COVID-19: Data from Japanese clusters
The early estimate of asymptomatic ratio has been reported as ranging from 8 to 54% (Nishiura et al., 2020). Besides, more than half of secondary transmissions with coronavirus disease 2019 (COVID-19) are considered to occur from asymptomatically infected people (Johansson et al., 2021). The estimate reflects the substantial number of secondary transmissions from pre-symptomatic individuals who eventually develop illness.Ascertainment rate of novel coronavirus disease (COVID-19) in Japan
As of March 1, 2020, a total of 58 countries had reported at least one confirmed case of novel coronavirus disease (COVID-19), and the cumulative number of deaths had reached 2977 persons across the world (WHO, 2020). To achieve appropriate countermeasures, it is vital to understand the current epidemiological situations of the COVID-19 epidemic.
