The virus is an RNA virus not a mRNA virus. MRNA is used to create specific proteins. The initial thought, by vax makers, was the mRNA was fragile and would quickly degrade. That turned out to be wrong. It lasted way longer and in some parts of the body. Net results are way more spike than a normal infection.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7173417/
Introduction to RNA Viruses
“The RNA virus group can be subdivided based on the type of RNA that serves as the genome. Positive or plus (+)-strand RNA viruses have genomes that are functional mRNAs.”
https://www.nature.com/articles/s41467-020-19883-7
“Similar to other coronaviruses, SARS-CoV-2 is an enveloped, positive sense, single stranded RNA virus “