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. 2021 May 25;47(7):786–789. doi: 10.1007/s00134-021-06414-1

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© The Author(s) 2021

Open AccessThis article is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License, which permits any non-commercial use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article's Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article's Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by-nc/4.0/.

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Fig. 1 — Technologies on which the main current COVID-19 vaccines or vaccine candidates are based. Inactivated vaccines such as Sinovac (CoronaVac®), Sinopharm (BBIBP-CorV®) or Bharat Biotech (BBV152/Covaxin®) are produced with traditional methods (similar to rabies or hepatitis A vaccines), where the SARS-CoV-2 virus is grown in cell culture, inactivated by β-propiolactone and adsorbed to alum (and other excipients). Current S-based vaccines consist of either (i) recombinant S protein (like hepatitis B vaccines), (ii) replication-deficient viral vectors expressing S, or (iii) mRNA encoding S. Because of an optimized design, these vaccines induce rapid and vigorous immune responses. For the subunit vaccines, recombinant S is produced in insect cells and formulated with saponin or other emulsions as adjuvant. In the case of NVX-CoV2373 by Novavax, S subunits are mounted on a synthetic protein-scaffold to further enhance their immunogenicity. The vector-based vaccines by AstraZeneca (AZD1222/Covishield®), Gamalenya (Gam-COVID-Vac/Sputnik V®) or Johnson & Johnson (Ad26.COV2.S/JNJ-78436735) use modified replication-deficient adenoviruses (respectively chimpanzee AdV; a combination of AdV 26 and AdV5; Adv26) to deliver an expression cassette for the copy DNA encoding for S (alike established e.g. for gene therapy). For the novel mRNA approach, synthetic mRNA encoding for S is encapsulated in lipid nanoparticles. Representative mRNA vaccines are BNT162b2 (Comirnaty®) by Pfizer/BioNtech, mRNA-1273 by Moderna and CVnCoV by Curevax. All current COVID-19 vaccines are administered by intramuscular injection; following a two-dose regimen (with as exception Ad26.COV2.S as single dose). For further information, see Kyriakidis et al. NPJ Vaccines. (2021) https://doi.org/10.1038/s41541-021-00292-w