Children and youth infected with SARS-CoV-2 have milder disease than do adults and, even among those with the recently described multi-system inflammatory syndrome (MIS-C), mortality is rare. The reasons for the differences in clinical manifestations are unknown, but suggest that age-dependent factors may modulate the anti-viral immune response. We compared cytokine, humoral, and cellular immune responses in pediatric (children and youth, age < 24 years) (n=65) and adult (n=60) patients with COVID-19 at a metropolitan hospital system in New York City. The pediatric patients had a shorter length of stay, decreased requirement for mechanical ventilation and lower mortality compared to adults. The serum concentrations of IL-17A and IFN-γ, but not TNF-α or IL-6, were inversely related to age. Adults mounted a more robust T cell response to the viral spike protein compared to pediatric patients as evidenced by increased expression of CD25+ on CD4+ T cells and the frequency of IFN-γ+CD4+ T cells. Moreover, serum neutralizing antibody titers and antibody-dependent cellular phagocytosis were higher in adults compared to pediatric COVID-19 patients. The neutralizing antibody titer correlated positively with age and negatively with IL-17A and IFN-γ serum concentrations. There were no differences in anti-spike protein antibody titers to other human coronaviruses. Together these findings demonstrate that the poor outcome in hospitalized adults with COVID-19 compared to children may not be attributable to a failure to generate adaptive immune responses.

Objective To characterize the demographic and clinical features of pediatric SARS-CoV-2 syndromes and identify admission variables predictive of disease severity. Study design We conducted a multicenter, retrospective and prospective study of pediatric patients hospitalized with acute SARS-CoV-2 infections and multisystem inflammatory syndrome in children (MIS-C) at eight sites in New York, New Jersey, and Connecticut. Results We identified 281 hospitalized patients with SARS-CoV-2 infections and divided them into three groups based on clinical features. Overall, 143 (51%) had respiratory disease, 69 (25%) had MIS-C, and 69 (25%) had other manifestations including gastrointestinal illness or fever. Patients with MIS-C were more likely to identify as non-Hispanic black compared with patients with respiratory disease (35% versus 18%, P =.02). Seven patients (2%) died and 114 (41%) were admitted to the ICU. In multivariable analyses, obesity (OR=3.39, 95% CI:1.26-9.10, P =.02) and hypoxia on admission (OR=4.01; 95% CI:1.14-14.15; P =.03) were predictive of severe respiratory disease. Lower absolute lymphocyte count (OR=8.33 per unit decrease in 10 9 cells/L, 95% CI:2.32-33.33, P =.001) and higher C-reactive protein (OR=1.06 per unit increase in mg/dL, 95% CI:1.01-1.12, P =.017) were predictive of severe MIS-C. Race/ethnicity or socioeconomic status were not predictive of disease severity. Conclusions We identified variables at the time of hospitalization that may help predict the development of severe SARS-CoV-2 disease manifestations in children and youth. These variables may have implications for future prognostic tools that inform hospital admission and clinical management.

Background: COVID-19 is more benign in children compared to adults for unknown reasons. This contrasts with other respiratory viruses where disease manifestations are often more severe in children. We hypothesize that a more robust early innate immune response to SARS-CoV-2 protects against severe disease. Methods: Clinical outcomes, SARS-CoV-2 viral copies and cellular gene expression were compared in nasopharyngeal swabs obtained at the time of presentation to the Emergency Department from 12 children and 27 adults using bulk RNA sequencing and quantitative reverse transcription PCR. Total protein, cytokines and anti-SARS-CoV-2 IgG and IgA were quantified in nasal fluid.Results: SARS-CoV-2 copies, ACE2 and TMPRSS2 gene expression were similar in children and adults, but children displayed higher expression of genes associated with interferon signaling, NLRP3 inflammasome, and other innate pathways. Higher levels of IFN-2, IFN-, IP-10, IL-8, and IL-1 protein were detected in nasal fluid in children versus adults. Children also expressed higher levels of genes associated with immune cells whereas expression of those associated with epithelial cells did not differ in children versus adults. Anti-SARS-CoV-2 IgA and IgG were detected at similar levels in nasal fluid from both groups. None of the children required supplemental oxygen whereas 7 adults did (p=0.03); four adults died.Conclusions: These findings provide direct evidence of a more vigorous early mucosal immune response in children compared to adults and suggest that this contributes to favorable clinical outcomes.