Severe Pediatric COVID-19 and Multisystem Inflammatory Syndrome in Children From Wild-type to Population Immunity: A Prospective Multicenter Cohort Study With Real-time Reporting

Serum proteomics reveals hemophagocytic lymphohistiocytosis-like phenotype in a subset of patients with multisystem inflammatory syndrome in children

Children with Multisystem Inflammatory Syndrome in Children (MIS-C) can present with thrombocytopenia, which is a key feature of hemophagocytic lymphohistiocytosis (HLH). We hypothesized that thrombocytopenic MIS-C patients have more features of HLH. Clinical characteristics and routine laboratory parameters were collected from 228 MIS-C patients, of whom 85 (37%) were thrombocytopenic. Thrombocytopenic patients had increased ferritin levels; reduced leukocyte subsets; and elevated levels of ASAT and ALAT. Soluble IL-2RA was higher in thrombocytopenic children than in non-thrombocytopenic children. T-cell activation, TNF-alpha and IFN-gamma signaling markers were inversely correlated with thrombocyte levels, consistent with a more pronounced cytokine storm syndrome. Thrombocytopenia was not associated with severity of MIS-C and no pathogenic variants were identified in HLH-related genes. This suggests that thrombocytopenia in MIS-C is not a feature of a more severe disease phenotype, but the consequence of a distinct hyperinflammatory immunopathological process in a subset of children.

Should we be afraid of long-term cardiac consequences in children with multisystem inflammatory syndrome? Experience from subsequent waves of COVID-19

The purpose of the study was to assess and compare short- and long-term cardiac complications of the multisystem inflammatory syndrome in children (MIS-C) by predominant severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variants throughout the pandemic. The analysis of prospectively collected data comparing cardiac complications of MIS-C during and after hospitalization across the original/alpha, delta, and omicron waves. Cardiac complications were defined as cardiac failure with systolic function impairment or hypotension or abnormalities in echocardiographic findings (decrease in LVEF, FS, valvular insufficiency, pericardial effusion, or coronary artery abnormalities). A total of 120 patients with MIS-C admitted to the Children's Hospital of Krakow between November 1, 2020, and May 5, 2023, were included in the study (74 during original/alpha dominance, 31 delta, and 15 omicron). Patients in the omicron group were found to be younger than those in the alpha and delta groups (37 vs. 75 vs. 80 months, p = 0.03). The frequency of cardiac failure with systolic function impairment or hypotension was diagnosed more frequently in the original/alpha and delta groups than in the omicron group (44.59% vs. 41.94% vs. 13.33%, p = 0.08) also echocardiographic abnormalities changed, with rates of 60.8%, 35.5%, and 13.3% (p < 0.001) accordingly. The multivariable regression revealed an older age (OR = 1.19, 95% CI = 1.07-1.33, p = 0.002) as the only independent factors of cardiac failure with systolic function impairment or hypotension. In all patients, signs of cardiac failure resolved during the hospitalization. Moreover, in 98.3% of patients, all echocardiagraphic abnormalities resolved completely during the observation period.    Conclusion: The cardiac complications of MIS-C appeared to advance less severely in younger children during the Omicron outbreak. In long-term observation, symptoms of cardiac failure resolve completely. Similarly, also echocardiographic abnormalities normalize in the vast majority of patients. What is Known: • Knowledge about the long-term cardiac complications of MIS-C is still evolving and uncertain. • The greatest concern of MIS-C is cardiac complications, including cardiac failure and coronary artery dilatation. What is New: • Long-term observations revealed complete resolution of cardiac complications in the vast majority of patients with MIS-C, irrespective of the dominant variant. • Cardiac complications of MIS-C were less common in younger children during subsequent pandemic waves in our patient population.

Differences in the Clinical Manifestations and Host Immune Responses to SARS-CoV-2 Variants in Children Compared to Adults

The COVID-19 pandemic challenged the medical field to rapidly identify and implement new approaches to the diagnosis, treatment and prevention of SARS-CoV-2 infections. The scientific community also needed to rapidly initiate basic, translational, clinical and epidemiological studies to understand the pathophysiology of this new family of viruses, which continues to evolve with the emergence of new genetic variants. One of the earliest clinical observations that provided a framework for the research was the finding that, in contrast to most other respiratory viruses, children developed less severe acute and post-acute disease compared to adults. Although the clinical manifestations of SARS-CoV-2 infection changed with each new wave of the pandemic, which was dominated by evolving viral variants, the differences in severity between children and adults persisted. Comparative immunologic studies have shown that children mount a more vigorous local innate response characterized by the activation of interferon pathways and recruitment of innate cells to the mucosa, which may mitigate against the hyperinflammatory adaptive response and systemic cytokine release that likely contributed to more severe outcomes including acute respiratory distress syndrome in adults. In this review, the clinical manifestations and immunologic responses in children during the different waves of COVID-19 are discussed.