Summary As severe acute respiratory syndrome coronavirus 2 continues to spread worldwide, there have been increasing reports from Europe, North America, Asia, and Latin America describing children and adolescents with COVID-19-associated multisystem inflammatory conditions. However, the association between multisystem inflammatory syndrome in children and COVID-19 is still unknown. We review the epidemiology, causes, clinical features, and current treatment protocols for multisystem inflammatory syndrome in children and adolescents associated with COVID-19. We also discuss the possible underlying pathophysiological mechanisms for COVID-19-induced inflammatory processes, which can lead to organ damage in paediatric patients who are severely ill. These insights provide evidence for the need to develop a clear case definition and treatment protocol for this new condition and also shed light on future therapeutic interventions and the potential for vaccine development. Translations For the French, Chinese, Arabic, Spanish and Russian translations of the abstract see Supplementary Materials section.

Detection of asymptomatic or subclinical novel human coronavirus SARS-CoV-2 infection is critical for understanding the overall prevalence and infection potential of COVID-19. To estimate the cumulative prevalence of SARS-CoV-2 infection in China, we evaluated the host serologic response, measured by the levels of immunoglobulins M and G in 17,368 individuals, in the city of Wuhan, the epicenter of the COVID-19 pandemic in China, and geographic regions in the country, during the period from 9 March 2020 to 10 April 2020. In our cohorts, the seropositivity in Wuhan varied between 3.2% and 3.8% in different subcohorts. Seroposivity progressively decreased in other cities as the distance to the epicenter increased. Patients who visited a hospital for maintenance hemodialysis and healthcare workers also had a higher seroprevalence of 3.3% (51 of 1,542, 2.5-4.3%, 95% confidence interval (CI)) and 1.8% (81 of 4,384, 1.5-2.3%, 95% CI), respectively. More studies are needed to determine whether these results are generalizable to other populations and geographic locations, as well as to determine at what rate seroprevalence is increasing with the progress of the COVID-19 pandemic. Serologic surveillance has the potential to provide a more faithful cumulative viral attack rate for the first season of this novel SARS-CoV-2 infection.The novel human coronavirus SARS-CoV-2 is a highly contagious virus, and its disease, COVID-19, can lead to significant morbidity and mortality in a proportion of patients 1-3 . On 12 March 2020, the World Health Organization declared it a global pandemic 4 . As of 12 May 2020, there were more than 4.2 million confirmed infections globally in more than 180 countries with over 290,000 deaths (https://www.arcgis.com/apps/opsdashboard/index.html#/ bda7594740fd40299423467b48e9ecf6).Detection of SARS-CoV-2 in asymptomatic individuals 5,6 suggests that subclinical active infection might be an important contributor to this outbreak. Currently, reported cases of COVID-19 are mainly limited to symptomatic individuals, those having close

A severe respiratory ongoing outbreak of pneumonia associated with 2019 novel coronavirus was recently emerged in China. Here, we reported the epidemiological, clinical, laboratory and radiological characteristics of 19 suspect cases. We compared J o u r n a l P r e -p r o o f

ObjectiveCompare paediatric COVID-19 disease characteristics, management and outcomes according to World Bank country income level and disease severity.DesignSystematic review and meta-analysis.SettingBetween 1 December 2019 and 8 January 2021, 3350 articles were identified. Two reviewers conducted study screening, data abstraction and quality assessment independently and in duplicate. Observational studies describing laboratory-confirmed paediatric (0–19 years old) COVID-19 were considered for inclusion.Main outcomes and measuresThe pooled proportions of clinical findings, treatment and outcomes were compared according to World Bank country income level and reported disease severity.Results129 studies were included from 31 countries comprising 10 251 children of which 57.4% were hospitalised. Mean age was 7.0 years (SD 3.6), and 27.1% had a comorbidity. Fever (63.3%) and cough (33.7%) were common. Of 3670 cases, 44.1% had radiographic abnormalities. The majority of cases recovered (88.9%); however, 96 hospitalised children died. Compared with high-income countries, in low-income and middle-income countries, a lower proportion of cases were admitted to intensive care units (ICUs) (9.9% vs 26.0%) yet pooled proportion of deaths among hospitalised children was higher (relative risk 2.14, 95% CI 1.43 to 3.20). Children with severe disease received antimicrobials, inotropes and anti-inflammatory agents more frequently than those with non-severe disease. Subgroup analyses showed that a higher proportion of children with multisystem inflammatory syndrome (MIS-C) were admitted to ICU (47.1% vs 22.9%) and a higher proportion of hospitalised children with MIS-C died (4.8% vs 3.6%) compared with the overall sample.ConclusionPaediatric COVID-19 has a favourable prognosis. Further severe disease characterisation in children is needed globally.