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 (preprint)

Importance: Understanding the susceptibility and infectiousness of children and adolescents in comparison to adults is important to appreciate their role in the COVID-19 pandemic. Objective: To 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 Sources: We searched EMBASE, PubMed and medRxiv up to January 2022. Additional studies were identified through contacting subject experts. Study Selection: Two 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 Synthesis: Two 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 Measures: Odds 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. Results: Twenty-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 Relevance: When 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.

Transmission roles of symptomatic and asymptomatic COVID-19 cases: a modeling study (preprint)

ObjectiveAge-dependent asymptomatic and symptomatic transmission dynamics of COVID-19 have not been well quantified due to limited data. MethodsThrough a population-based surveillance network, we collected data on 1342 confirmed cases with a 90-days follow-up for all asymptomatic cases. ResultsThe difference in transmissibility of a symptomatic and asymptomatic case depended on age and was most distinct for the middle-age groups. The asymptomatic cases had a 66.72% lower transmissibility rate than symptomatic cases, and 74.10% (95%CI: 65.85% - 80.72%) of all asymptomatic cases were missed in detection. The average proportion of asymptomatic cases was 28.22% (95%CI: 22.97% - 34.56%). Simulation showed that the burden of asymptomatic transmission increased as the epidemic continued and could potentially dominate the spreading. ConclusionAsymptomatic COVID-19 cases play a significant role in transmission. Vaccine Strategies prioritizing the population between 30-60 years old are likely to have the most population-level benefits.