Or just that we can't stabilize/synthesize the protein usefully in a vaccine with existing techniques. One of the big deals of mRNA is that because you get the

Or just that we can't stabilize/synthesize the protein usefully in a vaccine with existing techniques. One of the big deals of mRNA is that because you get the proteins made in-vivo (in the body), you inherit all the body's machinery to do this naturally - after all, viral replication requires using that exact same machinery in order to replicate up the viral proteins in the first place.