when you receive a vaccine it helps your body to create antibodies. antibodies are the body's defenses that fight off any foreign substances (germs). although your body can create antibodies on its own most of the vaccine-preventable diseases cause severe illness and even death before enough antibodies are produced. immunization (vaccination) schedule vaccines work best when they are given at certain ages. for example the measles vaccine is not usually given until a child is at least one year old. if it is given earlier than that it may not work as well. on the other hand the dtap vaccine should be given over a period of time in a series of properly spaced doses. the routine childhood immunization schedule is published each year by the cdc.
how do vaccines work?