Bacteria, viruses and other germs threaten your body every day. But when
a disease-causing microorganism enters your body, your immune system
mounts a defense, producing proteins called antibodies to fight off the
invader. The goal of your immune system is to prevent illness by
destroying the foreign invader or rendering it harmless.
Vaccines stimulate your body's immune system.
Vaccine-induced immunity results after you receive a vaccine. The
vaccine triggers your immune system's infection-fighting ability and
memory without exposure to the actual disease-producing germs. A vaccine
contains a killed or weakened form or derivative of the infectious
germ. When given to a healthy person, the vaccine triggers an immune
response. The vaccine makes your body think that it's being invaded by a
specific organism, and your immune system goes to work to destroy the
invader and prevent it from infecting you again.