Why will you NOT get sick from a vaccine? A. The pathogens it contains are dead or weakened. B. The antibodies you produce after getting the vaccine kill the injected pathogens. C. It does not contain any pathogens. D. It is medicine that kills pathogens, so it would kill any infection as well.
The vaccine is dead/weakened pathogens injected to cause antibodies. These antibodies will recognize the pathogens if they see them and fight them off.