Pediatric COVID-19 patients in South Brazil show abundant viral mRNA and strong specific anti-viral responses

COVID-19 manifests as a milder disease in children than adults, but the underlying mechanisms are not fully characterized. Here we assess the difference in cellular or humoral immune responses of pediatric and adult COVID-19 patients to see if these factors contribute to the severity dichotomy. Children’s non-specific immune profile is dominated by naive lymphocytes and HLA-DRhighCX3CR1low dendritic cells; meanwhile, children show strong specific antibody and T cell responses for viral structural proteins, with their T cell responses differing from adults by having weaker CD8+TNF+ T cells responses to S peptide pool but stronger responses to N and M peptide pools. Finally, viral mRNA is more abundant in pediatric patients. Our data thus support a scenario in which SARS-CoV-2 infected children contribute to transmission yet are less susceptible to COVID-19 symptoms due to strong and differential responses to the virus.


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Antibodies
Antibodies used A prospective cohort study was carried out at Hospital Moinhos de Vento and at Hospital Restinga e Extremo Sul, both in Porto Alegre, southern Brazil. A convenience sample of adults and children older than 2 months were enrolled from June to December 2020 at either the outpatient clinics (OPC), emergency rooms (ER), or hospitalized.We have recruited a total of 92 patients (25 children; 34 adults with mild disease -AMD; and 33 adults with severe disease -ASD). All subjects had COVID-19 confirmed by PCR.
No raw data was excluded from the analysis. For PCA analysis, redundant variables were excluded when they did not add information, as that is stated in the manuscript.
RNA extracted by nasal swabs is still available for replications. From blood samples, plasma is still available for replication, but few patients still have cryopreserved cells left. When cells were available, tests were performed twice. Due to limited amount of blood obtained by some individuals, their tests were performed only once. All attempts at replication were successful.
This was an observational study to generate hypotheses, and not of a randomized, experimental design (as in testing drug effects, for example). Thus, randomization was not applicable.
This was an observational study to generate hypotheses, and not of a randomized, experimental design (as in testing drug effects, for example). Thus, blinding was not applicable. A prospective cohort study was carried out at Hospital Moinhos de Vento and at Hospital Restinga e Extremo Sul, both in Porto Alegre, southern Brazil. A cohort of 92 patients (25 children; 34 adults with mild disease -AMD; and 33 adults with severe disease -ASD). Median age was 9 for children, 37.8 for AMD and 60.8 for ASD. Mainly of female sex and Caucasian. All patients' characteristics are presented in table 1 A convenience sample of adults and children older than 2 months were enrolled from June to December 2020 at either the outpatient clinics (OPC), emergency rooms (ER), or hospitalized.Subjects were screened if presenting cough and/or axillary temperature #37.8ºC and/or sore throat. Both blood samples and respiratory samples collected through nasopharyngeal swabs were obtained at enrollment. Only patients with the clinical diagnosis of COVID-19 and SARS-CoV-2 infection confirmed by RT-PCR were included in the study. Clinical and demographic data were collected at inclusion, following a standardized protocol. Disease severity was classified according to the World Health Organization classification after completing the follow-up questionnaire. In this study there was no self-selection bias in the recruitment of the participants This study was approved by the Institutional Review Board (IRB 30749720.4.1001.5330) at Hospital Moinhos de Vento and by the Ethics Committee at Universidade Federal de Ciências da Saúde (CAAE 30749720.4.3001.5345). Legal consent was obtained from all participants or their legal guardians. The study was conducted according to good laboratory practices and following the Declaration of Helsinki.
Both blood samples and respiratory samples collected through nasopharyngeal swabs were obtained at enrollment. We