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By Mayo Clinic Staff

Your body is built to fight germs that can make you sick. Most of the time, your immune system can stop bacteria and viruses before they cause serious illness.

But sometimes a new germ appears that your body hasn't seen before. When that happens, your immune system may not react quickly enough to protect you.

Vaccines help fill that gap. They safely teach your immune system to recognize certain germs and respond faster. This training makes you less likely to get very sick.

Ever wonder how these shots actually work? It comes down to the different types of vaccines and the ways they train your immune system.