The way the various vaccine platforms work can be summarised as follows:2 

• Inactivated or weakened virus vaccines use a modified form of the virus that will not cause disease but will still generate an immune response.
• Protein-based vaccines use harmless fragments of proteins or the viral capsule to mimic the virus and generate an immune response.
• Viral vector vaccines use a genetically engineered virus that cannot cause disease itself but produces allergen proteins to generate an immune response.
• RNA and DNA vaccines, the newest type of vaccines, use genetically engineered RNA or DNA to generate an antigen that will prompt an immune response. 

DNA and RNA vaccines use the enzymes, ribosomes and other apparatus in host cells to translate the introduced proteins and produce intracellular antigens. A lipid coating around the DNA/RNA protein aids the vaccine’s entry through the cell membrane, while modified nucleotides or nucleosides (the building blocks of RNA and DNA) may be included to delay degradation. Replicon RNA describes genetic code which can self-replicate.4,5 
DNA vaccines enter the cell nucleus, enabling the host cells’ RNA polymerases to produce mRNA which is secreted into the cytoplasm where it is used to produce the desired antigen. DNA vaccines should not integrate into host cell DNA but will be degraded by normal cellular processes.4 
Messenger RNA (mRNA) will not enter the host cell’s nucleus, being processed entirely in the cytoplasm. Circulating ribonucleases degrade any mRNA not taken directly into cells.4 
Covid-19 is the first time mRNA vaccines have been used for mass human population use, but animal models over the past decade have demonstrated the effectiveness of mRNA vaccines against influenza, Zika virus, rabies, and cytomegalovirus (CMV). mRNA vaccination is also being developed to trigger the immune system to specific cancer cells.6,7