Abstract:Objective To explore the clinical characteristics of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) Delta variant in children and youth. Methods Patients infected with SARS-CoV-2 Delta variant and treated in Guangzhou Eighth People's Hospital, Guangzhou Medical University from May 21 to June 18, 2021 were selected, they were divided into children group (2-14 years old) and youth group (15-35 years old), differences in clinical, laboratory indicators and chest CT imaging between two groups of patients were compared. Results There were 21 cases in children group and 24 cases in youth group, there was no severe cases in two groups. Children were characterized by family aggregation, the common type was more frequent in youth group than in children group (66.7% vs 33.3%, P < 0.05). Compared with youth group, cough (33.3% vs 87.5%), expectoration (33.3% vs 66.7%) and throat discomfort (28.6% vs 70.8%) were all lower in children group (all P < 0.05), the duration of fever in children was shorter (2.5 d vs 4 d, P < 0.05), however, there was no significant difference in fever (76.2% vs 83.3%) between two groups of patients. Compared with biochemical indicators of youth group, levels of C-reactive protein (CRP), serum amyloid A (SAA) and interleukin-6 (IL-6) in children group were lower at baseline (all P < 0.05), but levels of lymphocyte (LYM), eosinophil (EOS), lactate dehydrogenase (LDH) and creatine kinase isoenzyme (CK-MB) were higher; at the first week, CRP and SAA were lower, but LYM, EOS, LDH and CK-MB were higher in children group (all P < 0.05). Elevation of CK-MB and LDH were more frequent in children at baseline (both P < 0.05). In children group, LYM decreased in 5 cases (23.8%) and EOS decreased in 3 cases (14.3%) at baseline, but both LYM and EOS returned to normal at the first week. Chest CT showed that 7 cases (33.3%) had pulmonary infection in children group, mainly unilateral involvement; in youth group, 16 cases (66.7%) showed pulmonary infection, mainly bilateral lung involvement. The median time of nucleic acid negative conversion of SARS-CoV-2 was 17 (12, 25) days in children group and 19 (15, 21) days in youth group, prognosis of two groups of patients were good. Conclusion SARS-CoV-2 Delta variant of children are mainly chara-cterized by family aggregation. Compared with youth patients, respiratory symptoms, inflammatory reaction, the injury of immune cells and lung in children patients are slighter, while immune cells recover faster. Elevation of CK-MB and LDH are more frequent in children at baseline, and attention should be paid to the possibility of acute myocardial injury. It takes a long time for virus nucleic acid of SARS-CoV-2 to turn negative in youth and children patients, so it is necessary to extend the time of monitoring nucleic acid of upper respiratory tract.