Figure 4.

Vaccine platforms being employed for SARS-CoV-2 vaccine design. This figure illustrates the different vaccine approaches being taken for the design of human SARS-CoV-2 vaccines. Whole virus vaccines include both attenuated and inactivated forms of the virus and subunits of inactivated virus can also be used. Protein and peptide subunit vaccines are usually combined with an adjuvant in order to enhance immunogenicity. The main emphasis in SARS-CoV-2 vaccine development has been on using the whole spike protein in its trimeric form or components of it, such as the RBD region. Multiple non-replicating viral vector vaccines have been developed, particularly focused on adenovirus; while there has been less emphasis on the replicating viral vector constructs. Nucleic acid-based approaches include DNA and mRNA vaccines, often packaged into nanocarriers such as virus-like particles (VLPs) and lipid nanoparticles (LNPs). Nanoparticle and VLP vaccines can also have antigen attached to their surface or combined in their core. The immune cell therapy approach uses genetically modified SARS-CoV-2-specific cytotoxic T cells and dendritic cells expressing viral antigens to protect against SARS-CoV-2 infection. Each of these vaccine approaches has benefits and disadvantages in terms of cost and ease of production, safety profile and immunogenicity, and it remains to be seen which of the many candidates in development protect against COVID-19.