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. 2022 Jul 9;4(2):98–104. doi: 10.1016/j.jobb.2022.06.001

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© 2022 Published by Elsevier B.V. on behalf of KeAi Communications Co., Ltd.

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. 1 — Trend of COVID-19 epidemic. The global COVID-19 epidemic showed a periodic increase in 2021. COVID-19 epidemic formed a “peak-trough” cycle approximately every-four months, and it is currently in the fourth increasing phase.