Table 1.
Potential vaccine candidates developed for SARS-CoV and MERS-CoV.
| Vaccine platform | Immunogen | Animal model | Route of injection | Adjuvant | Advantage | Disadvantage |
|---|---|---|---|---|---|---|
| Inactivated | Whole virus (i) Inactivated by formaldehyde or gamma irradiation |
Mice | IM | Alum and CpG ODN | (i) Excellence in neutralizing Ab induction | (i) Possible cause hypersensitivity-type lung |
| (ii) Can be combined with different adjuvant | (ii) Possible Th2-bias | |||||
| (iii) Cannot employ cell-mediated immunity | ||||||
| Live-attenuated virus | Mutant MERS-CoV and SARS-CoV | Mice, rhesus macaques | IN, IP | — | (i) Excellence in the induction of T and B cell responses | (i) Risk of relapse |
| (ii) Site-directed mutagenesis can be tailor-made | (ii) Cold chain required | |||||
| (iii) Not suitable or sensitive population such as infants, immunocompromised, or elderly individuals | ||||||
| Subunit | Full-length spike, S1, RDB, nucleocapsid (i) Formulated with various adjuvants and/or fused with Fc |
Mice, rhesus macaques | SC, IM, IN | MF59, Ontanide, Freund's adjuvant, alum, monophosphoryl lipid A, Montanide ISA51, CpG ODN | (i) High safety profile | (i) Need appropriate adjuvant |
| (ii) Continuous production | (ii) Cost-effectiveness may change | |||||
| (iii) Induction of high titers of neutralizing antibodies | ||||||
| (iv) Local mucosal immune responses were observed in mice immunized through IN route | ||||||
| DNA | Full-length spike or S1 (i) IM follow by electroporation |
Mice, camels and rhesus macaques | IM | Without adjuvant | (i) Fast production | (i) Efficient delivery system required |
| (ii) Simple design and manipulation | (ii) Induce lower immune responses when compared with a live vaccine | |||||
| (iii) Initiate both B and T cell responses | ||||||
| Viral vector | Full-length spike or S1 (i) Vector used: ChAd or MVA |
Mice, Bactrian camels | IM | CD40L | (i) Excellence in immune induction | (i) Different inoculation routes may produce different immune responses |
| (ii) Possible TH2 bias | ||||||
| Virus-like particles | RDB, S, or coexpressing of S1, M, and E | Rhesus macaques, mice | IM | Alum, poly(I:C) CpG ODN | (i) Multimeric antigen display | (i) Need optimum assembly condition |
| (ii) Maintain virus particle structure |
RBD: a receptor-binding domain in S1; MVA: modified vaccinia virus Ankara; ChAdOx1: chimpanzee adenovirus; IM: intramuscular; IN: intranasal; IP: intraperitoneal; SC: subcutaneous.