Babies are born with protection against some diseases because their mothers pass antibodies (proteins made by the body to fight disease) to them before birth. Breastfed babies continue to get more antibodies in breast milk. But in both cases, the protection is temporary. Immunization (vaccination) is a way to create immunity to (protection from) some diseases. This is done by using small amounts of a killed or weakened germ that causes the disease. Germs can be viruses (such as the measles virus) or bacteria (such as pneumococcus). Vaccines stimulate the immune system to react as if there were a real infection. It fends off the "infection" and remembers the germ. Then, it can fight the germ if it enters the body later.