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. 2022 Apr 27;13:814365. doi: 10.3389/fimmu.2022.814365

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Copyright © 2022 Liu, Mao, Wu, He, Bian, Bai, Wang, Wang, Zhang, Liang and Xu

This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

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Key milestones in COVID-19 vaccine R&D, biweekly increases in COVID-19 cases worldwide, and total number of COVID-19 vaccine doses administered worldwide. (A) Timeline of the R&D of COVID-19 vaccines. Red flags indicate the key milestones in global COVID-19 vaccine R&D and vaccination with the corresponding dates indicated in parentheses. (B) Biweekly increases in COVID-19 cases worldwide with red stars denoting the time points of emergence of SARS−CoV−2 variants (data source: https://covid19.who.int/, https://cov-lineages.org/index.html). (C) Total number of COVID-19 vaccine doses administered worldwide (data source: https://github.com/owid/covid-19-data/blob/master/public/data/README.md).