RESULTS
A total of 287 articles were found in the systematic review of the literature (254 in PubMed and 38 in other databases). After removing duplicates, screening by title and abstract, 58 articles were selected for full-text evaluation, 14 were excluded for different reasons. A total 44 articles were chosen for qualitative analysis, 38 for quantitative analysis of clinical findings [17,18, 21-30,32-38,40,42-48,50-52,54-58,60,62] and 43 for quantitative analysis of illness severity severity[17,18,31-56,58,60-62].Figure 1.  All were observational studies, twenty-six studies were done in China [21-37,], five were from USA [18,39,50,59,60], five from Italy [40,44,47,56,57], three from Spain [49,51,61], two from France [48,62], one was made in Malaysia [38], Iraqi Kurdistan [41] and UK [17]. The main characteristics of included studies and individual risk of bias are shown in Table 1 .
Epidemiology
A total of 6026 children with confirmed or suspected COVID-19 were included. 55.25% cases were males. Age ranged from newborn to 21 years, a total of 5754 patients were distributed as follows: 19.09% (< 1 year), 17.18% (1-5 years), 20.17% (6-10 years) and 43.53% (>10 years) [21,27,29-35,38-48,50-52,54,56,59,61]. Supplementary Material . Mean incubation period was 6.33 (± 2.48) days. Fourteen studies noted 165 patients with comorbidities [17,21,26,27,30,34,39,41,47-49,51,57], the most common are neoplasms, overweight and obesity, cardiac diseases, neurological and chronic respiratory diseases, mostly asthma. In addition 5 studies reported 6 severe/critical cases with comorbidities, a teenager with obesity, one scholar with acute lymphoblastic leukemia, 3 infants with congenital cardiac disease, one infant with chronic wheezes. [21,27,30,49,58]. A total of 68.48% cases (526/768) had previous contact with an infected family member.  Diagnosis was performed with real time polymerase chain reaction (RT-PCR) by nasopharyngeal swab in 1656 patients, 110 patients were diagnosed by serum antibodies (IgM, IgG). [17,18,44,48,61,62]. Seven studies assessed the presence of SARS-CoV-2 in stools [25,29,30,32,45,48,61], finding 18.82% (32/170) positive cases. All RT-PCR tests in stool samples were made in confirmed cases of COVID-19.
Illness severity
Illness severity distribution among 3175 cases (2 lost) [31] were: asymptomatic 6% (CI95% 3-10%), I2 84.92% p<0.001 (all of them diagnosed after contact with family member), mild disease 28%(CI 95% 19-38%) I2 92.05% p<0.001,   moderate disease 33%(CI 95% 24-43%) I2 92.20% p<0.001, severe illness 2% (CI 95% 0-5%) I 77.52% p<0.001 and critical disease 3% (CI 95% 1-6%) with I2 90.04% and p<0.001 Figure 2 .
Hence approximately 89.73% cases in pediatric population were non-severe. Pooled Odds Ratio (OR) of severe or critical illness in children <1y was 2.07 (CI 95% 1.40-3.05) p<0.001, but heterogeneity statistics were unable to calculate since a single study weighs almost 100% and in patients >10y pooled OR was 0.75 (CI 95% 0.16-3.43) but it was not statistically significant.