Abstract: Objectives: This systematic review and meta-analysis aimed to estimate the age-specific proportion of asymptomatic SARS-CoV-2 infected persons by year of age. Methods: We searched PubMed, Embase, medRxiv and Google Scholar on 10 September 2020 and 1 March 2021. We included studies conducted during January to October 2020, prior to routine vaccination against COVID-19. Since we expected the relationship between the asymptomatic proportion and age to be non-linear, multilevel mixed-effects logistic regression (QR decomposition) with a restricted cubic spline was used to model asymptomatic proportions as a function of age. Results: A total of 38 studies were included in the meta-analysis. In total, 6556 out of 14850 cases were reported as asymptomatic. The overall estimate of the proportion of people who became infected with SARS-CoV-2 and remained asymptomatic throughout infection was 44.1% (6556/14850, 95%CI 43.3%-45.0%). The asymptomatic proportion peaked in adolescents (36.2%, 95%CI 26.0%-46.5%) at 13.5 years, gradually decreased by age and was lowest at 90.5 years of age (8.1%, 95%CI 3.4%-12.7%). Conclusions: Given the high rates of asymptomatic carriage in adolescents and young adults and their active role in virus transmission in the community, heightened vigilance and public health strategies are needed among these individuals to prevent disease transmission.

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