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Background: Multisystem inflammatory syndrome in children (MIS-C) occurs after SARS-CoV-2 infection, with gastrointestinal symptoms a prominent feature. This syndrome has been proposed to be triggered by persistent SARS-CoV-2 antigenemia due to increased intestinal epithelial permeability. We obtained evidence for this in this study. Methods: In a single-centre study, we recruited 83 children and analysed blood samples to quantify the circulating markers of increased intestinal permeability following SARS-CoV-2 infection. Publicly available proteomics MIS-C datasets were also accessed to assess the evidence for increased intestinal permeability. We further quantified SARS-CoV-2 antigenemia and the humoral response to SARS-CoV-2 spike protein. Results: Following SARS-CoV-2 infection, healthy children demonstrated no dysregulation of the intestinal epithelial barrier. In MIS-C, considerable increases in markers of epithelial dysfunction were observed, with similar increases noted in febrile controls. Furthermore, we found little evidence of persistent SARS-CoV-2 antigenemia in MIS-C. Conclusions: Our results suggest that although increased intestinal epithelial permeability is a feature of MIS-C, it is not unique to the condition, and persistent SARS-CoV-2 antigenemia does not occur.

Summary: SARS-CoV-2 infections in children are generally asymptomatic or mild and rarely progress to severe disease and hospitalization. Why this is so remains unclear. Here we explore the potential for protection due to pre-existing cross-reactive seasonal coronavirus antibodies and compare the rate of antibody decline for nucleocapsid and spike protein in serum and oral fluid against SARS-CoV-2 within the pediatric population. No differences in seasonal coronaviruses antibody concentrations were found at baseline between cases and controls, suggesting no protective effect from pre-existing immunity against seasonal coronaviruses. Antibodies against seasonal betacoronaviruses were boosted in response to SARS-CoV-2 infection. In serum, anti-nucleocapsid antibodies fell below the threshold of positivity more quickly than anti-spike protein antibodies. These findings add to our understanding of protection against infection with SARS-CoV-2 within the pediatric population, which is important when considering pediatric SARS-CoV-2 immunization policies.