What exactly do you think is happening when you get SARS-CoV-2? Do you think your cells are not taking viral mRNA and using it to make proteins? That is exactly what a virus does – it hijacks certain parts of your body that don't know any better to do its bidding. That protein is going to be produced by your body whether you get the virus or you get the vaccine. The difference is that with the vaccine the spike protein is all your body is producing (and a limited amount at that), while with the real virus your body is contending with 29 proteins that can work together in concert.