A good vaccine trains your immune system without having many of the negative side effects of the disease. That's why when they are pushing this 'new mRNA vaccine' that just expresses the spike protein in recipients, they are reporting pain as a massive side effect. Like, no shit if you put a bunch of little spikes randomly circulating through someone's body that shit is going to hurt. It's like the people that designed and approved the vaccine have never heard of sickle cell anemia.