To be fair, we've been shooting mRNA into people for medical research since about 1992. Early attempts were for gene therapy, but the approach has been abandoned because the mRNA breaks down so quickly. Beyond that, the mRNA is telling your cell to produce structural proteins. We've been using structural proteins in vaccines for AGES. Random bits of structural proteins are circulation around your body, being broken down, recycled, and eliminated as waste all of the time. There's no reason to believe that this structural protein is dangerous by itself.

I can't figure out what these vaccines do that could even have long term effects beyond getting your immune system to recognize the protein.