[set fair (OP)]

ie which proteins. Specifically is the envelope protein E- protein included and would this be a sensible target? I'm surprised we haven't heard much about this protein. I guess there must be a good reason - anyone know why?

[evan_au]

Every virus has a different set of proteins, so vaccines for different viruses need to emulate different proteins in order to create an effective immune response.
- But a useful target is the protein by which a virus enters the human (or animal) cell. Gum that up with antibodies, and the virus can't infect a cell - these are called neutralising antibodies.

Ultimately, the mRNA vaccines are also protein vaccines - they expose a protein to the immune system, which then targets that protein with antibodies.
- The difference is that the mRNA sequence provides the template from which the target protein is manufactured by ribosomes.

If you are talking about COVID specifically:

Like other coronaviruses, SARS-CoV-2 has four structural proteins, known as the S (spike), E (envelope), M (membrane), and N (nucleocapsid) proteins; the N protein holds the RNA genome, and the S, E, and M proteins together create the viral envelope.

The only proteins exposed to the immune system are S, E & M.
- Most existing vaccines target the Spike (S) protein, to create neutralising antibodies.
- Someone who has been infected will also develop antibodies to E & M proteins. These won't neutralise the virus, but they will draw the attention of the immune system to an infection.