Vaccine platforms
A vaccine platform determines what is delivered to generate an immune response. Whole-virus, viral-vector, protein-based and nucleic-acid approaches differ in whether they supply viral particles, antigenic proteins or genetic instructions for producing those proteins.
Whole-virus vaccines
Whole-virus vaccines present viral particles to the body. Inactivation can use heat or chemicals. Weakening a virus can instead involve repeated passage through cell lines: adaptation to those cells can make it weaker in another host or species.
Viral-vector vaccines
A viral-vector vaccine uses another virus as a carrier, with sections of the target virus's genome inserted into the vector's genome. Viral vectors can be self-replicating or non-replicating.
Protein-based vaccines
Protein-based approaches supply antigenic proteins, such as coronavirus spike or membrane proteins or subunits, to induce an immune response. Virus-like particles are empty viral shells without a genome and are therefore non-infectious; they can display an antigen such as spike protein on their surface, which is expected to activate the immune system.
Nucleic-acid vaccines and delivery
Nucleic-acid vaccines provide DNA or RNA so that the recipient's cells produce viral proteins. In an mRNA approach, a formulation carries RNA into host cells, where it is released and translated into proteins that induce an immune response.
RNA delivery needs protection against RNases, enzymes that readily digest RNA. A nanoformulation, such as a lipid formulation, protects the genetic material until it reaches host cells and is released. The protective formulation can carry RNA or DNA.