When a microbe first enters our immune system, our immune cells respond against it and then remember it specifically. So the next time that particular microbe or its close relatives enter the body, the immune system responds with even greater vigor. This eliminates the infection even more quickly than the first time. This phenomenon stands as the basic principle for an important methodology of preventing diseases. This method is called as
Vaccination helps the immune system to develop a memory for a particular infection by putting something that mimics the microbe we want to vaccinate against, into the body. This does not actually cause the disease but the antibodies for the particular microbe will be already present in the memory cells of the body. This would prevent any subsequent exposure to the infecting microbe from turning into actual disease.