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Objectives: Although long COVID-19 is widely recognized in adults, less information is available about this condition in children, especially in developing countries. Here, we studied the long-term symptoms of SARS-CoV-2 infection beyond 3 months and the associated risk factors in a pediatric population., Methods: This observational study included 639 Argentinian children and adolescents with previously confirmed COVID-19 from June 2020-June 2021 and 577 children without previous COVID-19. Parents completed a survey about symptoms that their child had for >3 months after the diagnosis of SARS-CoV-2 infection., Results: At least one persistent symptom was observed more frequently in children with previous COVID-19 than in the non-COVID-19 group (34% vs 13%, P <0.0001). SARS-CoV-2 infection increased the risk of headache, dizziness, loss of taste, dyspnea, cough, fatigue, muscle pain, and loss of weight by three- to seven-fold. The loss of smell was only reported in infected children. After controlling for the other variables, older age, symptomatic COVID-19, and comorbidities were independent predictors of long-term symptoms., Conclusions: One-third of children experienced persistent symptoms after COVID-19. Older age, symptomatic infection, and comorbidities were shown to be risk factors for long COVID-19. Pediatric long COVID-19 is a new condition that requires further investigation., Competing Interests: Declaration of competing interest The authors have no competing interest to declare., (Copyright © 2023 The Author(s). Published by Elsevier Ltd.. All rights reserved.)

There is a paucity of reports on the characteristics of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection in infants, because most studies have grouped infants with older children. We analyzed the viral loads of 45318 SARS-CoV-2-positive nasopharyngeal swab samples obtained in Buenos Aires, Argentina. Infants younger than 6 months presented higher viral loads than any other age group. Children older than 6 months showed significantly lower viral loads, similar to those founds in adults. This observation raises new questions regarding the role of infants in the spreading of SARS-CoV-2 infection., (© The Author(s) 2021. Published by Oxford University Press for the Infectious Diseases Society of America. All rights reserved. For permissions, e-mail: journals.permissions@oup.com.)

Background: Most children and youth develop mild or asymptomatic disease during severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection. However, a very small number of patients suffer severe Coronavirus induced disease 2019 (COVID-19). The reasons underlying these different outcomes remain unknown., Methods: We analyzed three different cohorts: children with acute infection (n=550), convalescent children (n=138), and MIS-C (multisystem inflammatory syndrome in children, n=42). IgG and IgM antibodies to the spike protein of SARS-CoV-2, serum-neutralizing activity, plasma cytokine levels, and the frequency of circulating Follicular T helper cells (cTfh) and plasmablasts were analyzed by conventional methods., Findings: Fifty-eight percent of the children in the acute phase of infection had no detectable antibodies at the time of sampling while a seronegative status was found in 25% and 12% of convalescent and MIS-C children, respectively. When children in the acute phase of the infection were stratified according disease severity, we found that contrasting with the response of children with asymptomatic, mild and moderate disease, children with severe COVID-19 did not develop any detectable response. A defective antibody response was also observed in the convalescent cohort for children with severe disease at the time of admission. This poor antibody response was associated to both, a low frequency of cTfh and a high plasma concentration of inflammatory cytokines., Interpretation: A weak and delayed kinetic of antibody response to SARS-CoV-2 together with a systemic pro-inflammatory profile characterize pediatric severe COVID-19. Because comorbidities are highly prevalent in children with severe COVID-19, further studies are needed to clarify their contribution in the weak antibody response observed in severe disease., Funding: National Agency for Scientific and Technological Promotion from Argentina (IP-COVID-19-0277 and PMO-BID-PICT2018-2548)., Competing Interests: Declaration of Competing Interest None., (Copyright © 2021 The Author(s). Published by Elsevier B.V. All rights reserved.)

Background: Perhaps reflecting that children with COVID-19 rarely exhibit severe respiratory symptoms and often remain asymptomatic, little attention has been paid to explore the immune response in pediatric COVID-19. Here, we analyzed the phenotype and function of circulating neutrophils from children with COVID-19., Methods: An observational study including 182 children with COVID-19, 21 children with multisystem inflammatory syndrome (MIS-C), and 40 healthy children was performed in Buenos Aires, Argentina. Neutrophil phenotype was analyzed by flow cytometry in blood samples. Cytokine production, plasma levels of IgG antibodies directed to the spike protein of SARS-CoV-2 and citrullinated histone H3 were measured by ELISA. Cell-free DNA was quantified by fluorometry., Findings: Compared with healthy controls, neutrophils from children with COVID-19 showed a lower expression of CD11b, CD66b, and L-selectin but a higher expression of the activation markers HLA-DR, CD64 and PECAM-1 and the inhibitory receptors LAIR-1 and PD-L1. No differences in the production of cytokines and NETs were observed. Interestingly, the expression of CD64 in neutrophils and the serum concentration of IgG antibodies directed to the spike protein of SARS-CoV-2 distinguished asymptomatic from mild and moderate COVID-19., Interpretation: Acute lung injury is a prominent feature of severe COVID-19 in adults. A low expression of adhesion molecules together with a high expression of inhibitory receptors in neutrophils from children with COVID-19 might prevent tissue infiltration by neutrophils preserving lung function., Funding: This study was supported by the Ministry of Science and Technology (National Agency for Scientific and Technological Promotion, IP-COVID-19-0277 and PMO BID PICT 2018-2548), and University of Buenos Aires from Argentina (20020170100573BA)., Competing Interests: Declaration of Competing Interest The authors have declared that no conflict of interest exists., (Copyright © 2021 The Authors. Published by Elsevier B.V. All rights reserved.)

In natural killer cells, killer immunoglobulin-like receptors (KIRs) loci code for either inhibitory or activating receptors, and according to the number of genes present in each individual, it is possible to identify a high rate of polymorphism in the populations. We performed KIR typing by polymerase chain reaction-sequence-specific oligonucleotide probing in 402 Argentinean Caucasoid and in two Amerindian populations (101 Wichis and 54 Chiriguanos) from the North of Argentina. KIR2DL4, KIR3DL2, KIR3DL3 and KIR3DP1 were always present, whereas the frequencies of KIR2DL1, KIR2DL3, KIR2DS4, KIR3DL1 and KIR2DP1 ranged between 84% and 96%. The frequencies of KIR2DS2, KIR2DL2, KIR2DL5, KIR2DS5, KIR2DS1 and KIR3DS1 ranged between 41% and 62%. The KIR2DS3 with a frequency of 29% in Argentinean Caucasoid population was present at a very low frequency in Amerindian populations. Haplotype segregation studies performed in 10 Wichi families showed the presence of only three haplotypes: A, B5 and B1. The Amerindian populations showed several similarities to Asian but not to Caucasoid populations with regard to the frequency of KIR2DS3, full-length KIR2DS4 gene and KIR2DL4 alleles.