Background: The clinical characteristics and outcome of COVID-19 in children are different from those in adults. We aimed to describe the characteristics of infants under 1 year of age (excluding newborns) with COVID-19.

Methods: We retrospectively retrieved data of 36 infants with SARS-CoV-2 infection in Wuhan Children’s Hospital from January 26 to March 22, 2020. Clinical features, chest imaging findings, laboratory tests results, treatments and clinical outcomes were analyzed.

Results: The mean age of the infected infants was 6.43 months, with a range of 2–12 months. 61.11% of the patients were males and 38.89% females. 86.11% of the infants were infected due to family clustering. Cough (77.78%) and fever (47.22%) were the most common clinical manifestations. Chest CT scan revealed 61.11% bilateral pneumonia and 36.11% unilateral pneumonia. 47.22% of the infants developed complications. Increased leucocytes, neutrophils, lymphocytes, and thrombocytes were observed in 11.11, 8.33, 36.11 and 44.44% of infants, respectively. Decreased leucocytes, neutrophils, thrombocyte and hemoglobin were observed in 8.33, 19.44, 2.78 and 36.11% of infants, respectively. Increased C-reactive protein, procalcitonin, lactate dehydrogenase, alanine aminotransferase, creatine kinase and D-dimer were observed in 19.44, 67.74, 47.22, 19.44, 22.22 and 20.69% of infants, respectively. Only one infant had a high level of creatinine. Co-infections with other respiratory pathogens were observed in 62.86% of infants. CD3 (20.69%), CD4 (68.97%), CD19 (31.03%) and Th/Ts (44.83%) were elevated; CD8 (6.9%) and CD16+CD56 (48.28%) was reduced. IL-4 (7.69%), IL-6 (19.23%), IL-10 (50%), TNF-α (11.54%) and IFN-γ (19.23%) were elevated. Up to March 22, 97.22% of infants recovered, while a critical ill infant died. When the infant’s condition deteriorates rapidly, lymphocytopenia was discovered. Meanwhile, C-reactive protein, D-dimer, alanine aminotransferase, creatine kinase, creatinine, IL-6 and IL-10 increased significantly.