Six researchers in three groups of two (Group 1: Zijun Wang, Qianling Shi; Group 2: Siya Zhao, Qi Zhou; Group 3: Yuyi Tang, Weiguo Li) retrieved and selected studies, extracted and analyzed data, and interpreted the results. Group 1 focused on remdesivir in treating children and adolescents with COVID-19, Group 2 focused on glucocorticoids in treating children and adolescents with severe COVID-19 and Group 3 focused on IVIG in treating children and adolescents with MIS-C. We reported our study in accordance to the Preferred Reporting Items for Systematic Reviews and Meta Analyses (PRISMA) 2020 guidelines. [19] (Supplementary File 1)
2.1 Search strategy
Two researchers in each group independently searched for literature using MEDLINE (via PubMed), Web of Science, the Cochrane library, China Biology Medicine (CBM), China National Knowledge Infrastructure (CNKI), Wanfang Data, and WHO COVID-19 database (https://search.bvsalud.org/global-literature-on-novel-coronavirus-2019-ncov/), ClinicalTrials.gov (https://clinicaltrials.gov/), MedRxiv (https://www.medrxiv.org/), BioRxiv (https://www.biorxiv.org/), SSRN (https://www.ssrn.com/index.cfm/en/), and Google. The electronic search was supplemented by manually examining the reference lists of the identified studies. In addition, emails were sent to the authors of studies to request available data that may be useful for our systematic review. The data search was from December 2019 to August 2021 without language limitations.
The researchers in groups 1, 2, and 3 used “remdesivir,” “corticosteroids,” and “intravenous immunoglobulin,” and its derivatives as retrieval terms, respectively. The terms were also combined with "COVID-19" and its derivatives using “AND”. For question 3, "MIS-C" and its derivatives were added as retrieval terms and combined with “AND” to improve the accuracy of the search. The search strategy can be found in Supplementary File 2.
2.2 Eligibility criteria
2.2.1 Inclusion criteria
Clinical question 1 (remdesivir)
Randomized controlled trials, non-randomized controlled trials, cohort studies, and case series of children and adolescents (≤ 18-year-old) with COVID-19 treated with remdesivir.
Clinical question 2 (glucocorticoids)
Randomized controlled trials, non-randomized controlled trials, cohort studies, and case series of COVID-19 children and adolescents (≤ 18 year) patients treated with glucocorticoids.
Clinical question 3 (IVIG)
1) The study population must meet the diagnostic criteria for MIS-C (WHO [20], CDC [21] or The Royal College of Paediatrics and Child Health [22]), and the included patients were not restricted by age, gender, disease course, race, region, and other factors.
2) The interventions/exposure included IVIG (intravenous immunoglobulin) vs. placebo or other treatment, or IVIG combined with other treatment vs. basic treatment.
3) Inclusion of studies was not restricted by the type of publication.
2.2.2 Exclusion criteria
Clinical question 1 (remdesivir)
1) Studies that failed to show the efficacy of remdesivir.
2) Case series that remdesivir was not administered to all the patients or subgroup comparison of remdesivir was unavailable.
3) Full text not available (example, studies inaccessible for download, conference abstract).
4) Duplications.
Clinical question 2 (glucocorticoids)
1) Studies that failed to show the efficacy of glucocorticoids.
2) Case series that glucocorticoid was not administered to all the patients or subgroup comparison of glucocorticoid was unavailable.
3) Full text not available (example, studies inaccessible for download, conference abstract).
4) Duplications.
Clinical question 3 (IVIG)
1) In vitro studies (example, animal experiments, in vitro experiments).
2) Full text not available (e.g., studies inaccessible for download, conference abstract).
3) Duplications.
2.3 Study selection
Two researchers in each group independently screened literature using the EndNote citation management software, and any disagreements were resolved by discussion. Before the formal screening process, researchers in each group randomly selected 50 studies to undertake a pilot study selection and ensure consistency in understanding the inclusion and exclusion criteria. Researchers used the inclusions and exclusions criteria first to screen the studies’ title and abstracts and excluded irrelevant literature. Then, the full text of the literature was reviewed to include the final eligible studies. Finally, the reasons for exclusion were recorded. The details of study selection are shown in the PRISMA 2020 flow diagram (Supplementary File 3).
2.4 Data extraction
Two researchers in each group extracted data independently in pairs, using a predefined data extraction form. Disagreements regarding the data extraction were resolved by discussion. The following information was extracted from the included studies: 1) baseline characteristics: author, year of publication, country, journal, number of included patients, gender, age, study design, and medication taken for COVID-19; 2) data extracted for clinical question 1: adverse events, severe adverse events, mortality, extracorporeal membrane oxygenation (ECMO) or invasive mechanical ventilation (IMV), length of hospital stay, hospital discharge, and symptom duration; 3) data extracted for clinical question 2: mortality, mechanical ventilation, and duration of pediatric intensive care unit (PICU) admission; and 4) data extracted for clinical question 3: number of patients who had treatment failure or secondary acute left ventricular dysfunction, number of patients who needed second-line treatment or hemodynamic support, the duration of PICU stay, isovolumic relaxation time, and the time to recovery of left ventricle ejection, cardiovascular dysfunction, left ventricular dysfunction, shock resulting in vasopressor use, use of adjunctive therapy, receipt of inotropic support or mechanical ventilation, reduction in the score for disease severity, rate of c-reactive protein (CRP) levels less than 60mg/L by day 3.
For dichotomous variables, the data of the number of events and the total of events were extracted. For continuous variables, mean, standard deviation, and the number of included patients were extracted. The median, quartile, maximum values, and minimum values were converted into mean and standard deviation using methods of estimating math [23]. Studies were excluded from the meta-analysis if the primary data was unavailable and showed the results of descriptive analysis of those studies.
2.5 Risk of bias assessment
Two reviewers in each group independently assessed the risk of bias of all included studies, and discrepancies were resolved by consensus. The risk of bias of the included randomized controlled trials was assessed using Cochrane’s risk of bias tool [24]. Potential sources of bias are examined according to six domains (including seven items): selection bias, performance bias, detection bias, attrition bias, reporting bias, and other biases. Each item was assessed as "low risk of bias," "high risk of bias," or "unclear." The risk of bias of included non-randomized controlled trials was assessed using the tool of ROBINS-I [25], which contains seven items (confounding, selection of participants into the study, classification of the intervention, deviations from intended interventions, missing data, measurements of outcomes, and selections of the reported result), each of which was assessed as "low risk," "moderate risk," "serious risk," "critical risk," and "no information". The Newcastle-Ottawa quality assessment scale [26,27] was used to assess the risk of bias of cohort studies. The scale contains eight items in three domains: selection, comparability, and outcome. The items were rated with an asterisk. The Quality Appraisal Checklist for Case Series Studies developed by the Institute of Health Economics was used to assess the risk of bias of case series studies [28]. The checklist contains twenty items in eight domains: study objective, study population, intervention and co-intervention, outcome measure, statistical analysis, results and conclusions, competing interests and sources of support, and supplement. Each item was evaluated with "yes" or "no".
2.6 Data synthesis
A meta-analysis using the STATA14 software when the outcomes of included studies were highly consistent and descriptive analyses when there was high heterogeneity of outcomes between the included studies. According to Cochrane Handbook, when the meta-analysis was conducted, a random-effects meta-analysis for all outcomes was presented [29]. For an included study with intervention group and control group, the odds ratios (ORs) and their 95% confidence interval (CI) were used to describe the effect of dichotomous variables while weighted mean differences (WMD) and their 95% CI were used to describe the effect of continuous variables. However, for an included study with only an intervention group, the effect sizes (ES) and their 95% CI were used to describe the effect of dichotomous variables while mean differences (MD) and their 95% CI were used to describe the effect of continuous variables. Statistical significance was set at <0.05 on both sides [30]. We used the chi-squared test and I² statistic were used to assess the level of statistical heterogeneity between the included studies, with p<0.05 and I² of less than 50% representing heterogeneity [30]. When substantial heterogeneity was detected, subgroup analyses by participant and study characteristics were used to compare pooled association estimates and heterogeneity. Furthermore, sensitivity analysis was used to detect potential outliers by omitting one estimate at a time and recalculating the pooled estimates. Publication bias was assessed through the funnel chart when the studies included in the meta-analyses were more than five [30].
2.7 Quality of the evidence assessment
Two reviewers in each group independently assessed the quality of evidence using the grading of recommendations assessment, development, and evaluation (GRADE) approach for meta-analysis. We created a "Summary of findings" table using GRADEpro to show effect estimates derived from the body of evidence (quality of evidence) by outcome [31,32]. Under the GRADE system, randomized controlled trials (RCTs) were initially assessed as high quality and observational studies as low quality. However, they were downgraded for reasons such as the risk of bias, inconsistency, indirectness, imprecision, publication bias, or upgraded for reasons such as the large magnitude of effect, dose-response gradient, and plausible confounding [33-38]. Thus, the quality of studies was rated as "high," "medium," "low," and "very low," reflecting the extent to which we are confident in the effect estimates.
Due to the peculiarity and public health significance of COVID-19, this study was not registered on the international registration platform PROSPERO.