Vaccines are simple measures that can be taken to help protect people from a variety of illnesses. Vaccines work by introducing a very small dose of a weakened or killed form of a specific virus or bacteria into the body. This helps the body generate an immune response and begin to form antibodies, as if it had been infected naturally. In turn, if a person does come into contact with that virus or bacteria later in life, the antibodies that were developed earlier can help fight it off before it has a chance to cause an infection. Vaccines are especially important for young children and the elderly, who have weaker immune systems and more vulnerable to infection. Vaccines can help protect individuals and the population as a whole from dangerous diseases.