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. 2022 Jan 31;15(3):297–306. doi: 10.1016/j.jiph.2022.01.015

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© 2022 The Author(s)

Since January 2020 Elsevier has created a COVID-19 resource centre with free information in English and Mandarin on the novel coronavirus COVID-19. The COVID-19 resource centre is hosted on Elsevier Connect, the company's public news and information website. Elsevier hereby grants permission to make all its COVID-19-related research that is available on the COVID-19 resource centre - including this research content - immediately available in PubMed Central and other publicly funded repositories, such as the WHO COVID database with rights for unrestricted research re-use and analyses in any form or by any means with acknowledgement of the original source. These permissions are granted for free by Elsevier for as long as the COVID-19 resource centre remains active.

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Fig. 7 — COVID-19 asymptomatic infection and the influencing factors Abbreviations: SIR, secondary infected rate; CI, confidence interval Note: ^a: Number of infected cases / total number of close contacts. * : Having removed studies with overlap data.