If you're exposed to a pathogen, you'll get infected. Immunity makes it so that your body recognizes the attacker and fights it. Vaccines and prior infection t

If you're exposed to a pathogen, you'll get infected. Immunity makes it so that your body recognizes the attacker and fights it. Vaccines and prior infection train the adaptive immune system to recognize pathogens so that the body can begin fighting the infection sooner. Some people's immune systems work less well than others, or due to situational factors, a person is more susceptible to infection and they become sick. People with immunity generally do far better at fighting the infection, being less ill and recovering faster. Nothing is perfect. Vaccines are better than getting sick or doing nothing.