BACKGROUND: Initial reports on severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infections in children suggested that very young age and comorbidities may increase risk of severe evolution, but these findings remained to be confirmed. We aimed to analyze the clinical spectrum of hospitalized pediatric SARS-CoV-2 infection and predictors of severe disease evolution. METHODS: We conducted a French national prospective surveillance of children hospitalized with SARS-CoV-2 infection. We included all children with confirmed SARS-CoV-2 infection in 60 hospitals during February 15 to June 1, 2020. The main outcome was the proportion of children with severe disease, defined by hemodynamic or ventilatory (invasive or not) support requirement. RESULTS: We included 397 hospitalized children with SARS-CoV-2 infection. We identified several clinical patterns, ranging from paucisymptomatic children, admitted for surveillance, to lower respiratory tract infection or multisystem inflammatory syndrome in children. Children <90 days old accounted for 37% of cases (145 of 397), but only 4 (3%) had severe disease. Excluding children with multisystem inflammatory syndrome in children (n = 29) and hospitalized for a diagnosis not related to SARS-CoV-2 (n = 62), 23 of 306 (11%) children had severe disease, including 6 deaths. Factors independently associated with severity were age ≥10 years (odds ratio [OR] = 3.4, 95% confidence interval: 1.1–10.3), hypoxemia (OR = 8.9 [2.6–29.7]), C-reactive protein level ≥80 mg/L (OR = 6.6 [1.4–27.5]). CONCLUSIONS: In contrast with preliminary reports, young age was not an independent factor associated with severe SARS-CoV-2 infection, and children <90 days old were at the lowest risk of severe disease evolution. This may help physicians to better identify risk of severe disease progression in children.

recently reported a favorable outcome of an acute chest syndrome (ACS) related to a SARS-Cov-2 infection treated with tocilizumab (TCZ), in a 45-year-old male patient with homozygous sickle cell disease (SCD). Following this successful observation, TCZ was administered to a teenage girl with SCD who developed a severe COVID-19 associating ACS and pulmonary embolism. This 16-year-old girl has a severe form of homozygous SCD with bilateral ischemic retinopathy. Given the recurrence of vaso-occlusive crises and abnormal transcranial doppler evaluations, she was treated with exchange transfusions from 5 to 11 years old, switched thereafter for hydroxyurea (22 mg/kg/day), with a favorable clinical outcome on vaso-occlusive events. She had no history of ACS or pulmonary hyper-

Background The extent to which very young children contribute to the transmission of SARS-CoV-2 is unclear. We aimed to estimate the seroprevalence of antibodies against SARS-CoV-2 in daycare centres that remained open for key workers' children during a nationwide lockdown in France. Methods Children and staff who attended one of 22 daycare centres during a nationwide lockdown in France (between March 15 and May 9, 2020) were included in this cross-sectional, multicentre, seroprevalence study. Hospital staff not occupationally exposed to patients with COVID-19, or to children, were enrolled in a comparator group. The primary outcome was SARS-CoV-2 seroprevalence in children, daycare centre staff, and the comparator group. The presence of antibodies against SARS-CoV-2 in capillary whole blood was measured with a rapid chromatographic immunoassay. We computed raw prevalence as the percentage of individuals with a positive IgG or IgM test, and used Bayesian smoothing to account for imperfect sensitivity and specificity of the assay. This study is registered with ClinicalTrials.gov, NCT04413968. Findings Between June 4 and July 3, 2020, we enrolled 327 children (mean age 1•9 [SD 0•9] years; range 5 months to 4•4 years), 197 daycare centre staff (mean age 40 [12] years), and 164 adults in the comparator group (42 [12] years). Positive serological tests were observed for 14 children (raw seroprevalence 4•3%; 95% CI 2•6-7•1) and 14 daycare centre staff (7•7%; 4•2-11•6). After accounting for imperfect sensitivity and specificity of the assay, we estimated that 3•7% (95% credible interval [95% CrI] 1•3-6•8) of the children and 6•8% (3•2-11•5) of daycare centre staff had SARS-CoV-2 infection. The comparator group fared similarly to the daycare centre staff; nine participants had a positive serological test (raw seroprevalence 5•5%; 95% CI 2•9-10•1), leading to a seroprevalence of 5•0% (95% CrI 1•6-9•8) after accounting for assay characteristics. An exploratory analysis suggested that seropositive children were more likely than seronegative children to have been exposed to an adult household member with laboratory-confirmed COVID-19 (six [43%] of 14 vs 19 [6%] of 307; relative risk 7•1 [95% CI 2•2-22•4]). Interpretation According to serological test results, the proportion of young children in our sample with SARS-CoV-2 infection was low. Intrafamily transmission seemed more plausible than transmission within daycare centres. Further epidemiological studies are needed to confirm this exploratory hypothesis.