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. 2020 Dec 9;9(2):693–701. doi: 10.1016/j.jaip.2020.11.054

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© 2020 American Academy of Allergy, Asthma & Immunology.

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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Study selection. PubMed, Embase, Web of Science, bioRxiv, and medRxiv databases were searched on July 21, 2020, for articles published since January 1, 2020. Another search was performed on August 18, 2020, to include eligible articles that were published between the 2 searches.