Susceptibility and infectiousness of SARS-CoV-2 in children versus adults, by variant (wild-type, Alpha, Delta): a systematic review and meta-analysis of household contact studies
Authors: Uthman Olalekan A. , Lyngse Frederik Plesner , Anjorin Seun , Hauer Barbara , Hakki Seran , Martinez Diego A. , Ge Yang , Jonnerby Jakob , Julin Cathinka Halle , Lin Gary , Lalvani Ajit , Loss Julika , Madon Kieran J , Martinez Leonardo , Næss Lisbeth Meyer , Page Kathleen R. , Prieto Diana , Robertson Anna Hayman , Shen Ye , Wurm Juliane , Buchholz Udo 
Published: August 2022

ABSTRACTImportanceUnderstanding the susceptibility and infectiousness of children and adolescents in comparison to adults is important to appreciate their role in the COVID-19 pandemic.ObjectiveTo determine SARS-CoV-2 susceptibility and infectiousness of children and adolescents with adults as comparator for three variants (wild-type, Alpha, Delta) in the household setting. We aimed to identify the effects independent of vaccination.Data SourcesWe searched EMBASE, PubMed and medRxiv up to January 2022. Additional studies were identified through contacting subject experts.Study SelectionTwo reviewers independently identified studies providing secondary attack rates (SAR) for SARS-CoV-2 infection in children (0-9 years), adolescents (10-19 years) or both compared with adults (20 years and older) derived from household data.Data Extraction and SynthesisTwo reviewers independently performed data extraction. We assessed risk of bias of included studies using a critical appraisal checklist and a random-effects meta-analysis model to pool association estimates.Main Outcomes and MeasuresOdds ratio (OR) for SARS-CoV-2 infection comparing children and adolescents with adults stratified by wild-type, Alpha, and Delta variant, respectively. Susceptibility was defined as the secondary attack rate (SAR) among susceptible household contacts irrespective of the age of the index case. Infectiousness was defined as the SAR irrespective of the age of household contacts when children/adolescents/adults were the index case.ResultsTwenty-eight studies (308,857 contacts) were included in the susceptibility analysis, for Delta only one (large) study was available. Compared to adults children and adolescents were less susceptible to the wild-type and Delta variant, but equally susceptible to the Alpha variant. In the infectiousness analysis, 21 studies (201,199 index cases) were included. Compared to adults, children and adolescents were less infectious when infected with the wild-type and Delta variant. Alpha variant-related infectiousness remained unclear, 0-9 year old children were at least as infectious as adults. SAR among household contacts was highest during circulation of the Alpha variant, lowest during wild-type circulation and intermediate during Delta circulation.Conclusions and RelevanceWhen considering the potential role of children and adolescents, for each variant susceptibility, infectiousness, age group and overall transmissibility need to be assessed to guide public health policy.KEY POINTSQuestionWhat is the evidence on the susceptibility and infectiousness of wild-type, Alpha and Delta variant of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) among children and adolescents compared with adults in the household setting?FindingsIn this systematic review and meta-analysis of 28 studies that included 308,857 household contacts, children and adolescents were less susceptible to the wild-type and Delta variant and likely equally susceptible to the Alpha variant of SARS-Cov-2. Children aged 0-9 years old infected with the Alpha variant may be more infectious than adults, but for adolescents, Alpha infectiousness is unclear. The overall secondary attack rate (SAR) rose substantially from wild-type to Alpha and dropped somewhat from Alpha to Delta.MeaningThe epidemiological role of children and adolescents towards SARS-CoV-2 may be influenced by susceptibility, infectiousness, variant, age group and overall (relative) contagiousness.