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. 2023 Feb 2;112(5):1345–1350. doi: 10.1016/j.xphs.2023.01.019

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© 2023 American Pharmacists Association. Published by Elsevier Inc. All rights reserved.

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 2 — Timeline of variants, vaccines, and protection against COVID-19. Several COVID-19 variants emerged over time around the globe. In US, the primary (two-dose regimen) resulted in protective immune response. However, with time this immune response waned off and immunization with a third dose helped boost the immune responses, however, the durability of this immune response is yet to be determined.