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Background Widespread respiratory infections with high morbidity rates caused by respiratory viruses represent a significant global public health problem. Our objective was to describe cases and deaths from severe acute respiratory infection (SARI) in Brazil over the past 8 y as well as changes in the distribution and risk of illness and death from SARI before and in the first year of the coronavirus disease 2019 (COVID-19) pandemic (FYP). Methods We performed a descriptive epidemiological study of hospitalized SARI cases and deaths between 2013 and 2020 in Brazil, separated into pre-pandemic (2013 to 2019) and FYP (2020). We estimate the increase in SARI cases and deaths in the FYP as well as the mortality and infection risks attributable to the FYP (MRAP and IRAP, respectively). Results In 2020, an excess of 425 054 cases and 109 682 deaths was observed, with a significant increase in the risk of falling ill and dying from SARI, with an IRAP of 200.06 and an MRAP of 51.68 cases per 100 000 inhabitants. The increase in SARI cases and deaths was particularly prominent among patients with COVID-19, the elderly, males, those self-identifying as mixed race and patients with heart disease and diabetes. We conclude that an important increase in morbidity and mortality due to SARI was observed in the FYP. More vulnerable groups and those living in the Southeast, North and Center-West regions of the country suffered the most.

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., Children often show milder COVID-19 symptoms, but the underlying mechanistic insights are still lacking. Here the authors profile both pediatric and adult cohorts of COVID-19 patients in Brazil to find that children exhibit higher viral load but stronger and biased cellular immunity, thereby serving clues for the differential responses in children.

Epidemiological evidence that COVID-19 manifests as a milder disease in children compared to adults has been reported by numerous studies, but the mechanisms underlying this phenomenon have not been characterized. It is still unclear how frequently children get infected, and/or generate immune responses to SARS-CoV-2. We have performed immune profiling of pediatric and adult COVID-19 patients in Brazil, producing over 38 thousand data points, asking if cellular or humoral immune responses could help explain milder disease in children. In this study, pediatric COVID-19 patients presented high viral titers. Though their non-specific immune profile was dominated by naive, non-activated lymphocytes, their dendritic cells expressed high levels of HLA-DR and were low in CX3CR1, indicating competence to generate immune responses that are not targeted to inflamed tissue. Finally, children formed strong specific antibody and T cell responses for viral structural proteins. Children’s T cell responses differed from adults in that their CD8+ TNFα+ T cell responses were low for S peptide but significantly higher against N and M peptide pools. Altogether, our data support a scenario in which SARS-CoV-2 infected children may contribute to transmission, though generating strong and differential responses to the virus that might associate with protection in pediatric COVID-19 presentation.