There is nothing like a graphic to explain a concept in molecular virology, such as how mRNA vaccines work.  The need to have mental images was explained in a previous post -- Wittgenstein and Cosmology

The BioNTech-Pfizer and Moderna vaccines use the mRNA that codes for the SARS-CoV-2 spike protein. This mRNA can be made in copious amounts in the laboratory but RNA is notoriously unstable and be easily degraded by RNAse enzymes and room themperature. The packaging into lipid nanoparticles adds to its stability and keeping it a freezing temperatures prevents the RNA being broken down by the ubiquitous presence of RNA degrading enzymes.

Injection of the vaccine into the arm delivers the mRNA into cells where the lipid nanoparticle fuses to the cellular lipid membrane layer and delivers the mRNA into the cytoplasm of the cell. The ribosomes bind to the mRNA and produce multiple copies of the CoV-2 spike protein. This spike protein migrates to the cell membrane and stimulates the immune response.

The main cost of the vaccine is the need to store the mRNA at low temperatures, the Moderna vaccine  can be maintained at most home or medical freezer temperatures while the BioNTech-Pfizer vaccine requires -70 degree ultra freezers.  No doubt there will be improvements in methods to stabilise these mRNA vaccines and reduce the costs.

This mRNA technique can also be used for future pandemics and the lipid nanoparticle provides a ‘plug and play’ for any virus. It potentially can be used for other immunotherapies such as for cancer, cystic fibrosis and other systemic and congenital diseases.

As Gwynne Dyer wrote in a recent column, “we can now be sure that the light at the end of this particular tunnel is not an oncoming train”.

For more graphics see NATURE Vol 580 pp 576-7, 2020
OR https://www.phgfoundation.org/briefing/rna-vaccines