The measles epidemic in the 90s illustrated that point all too well. Delaying immunizations until the start of school is not a good idea because they should be given to children before the age of two to protect them during their most vulnerable period. A vaccine is a preparation containing the weakened or killed microorganisms that cause a particular disease. When these substances are injected or taken orally, the body stimulates the immune system to produce the necessary defenses against that disease. Occasionally, because of the organisms introduced into the body, adverse reactions to vaccines may occur, but they are usually mild.
Serious reactions are rare.
The FDA recently approved Prevnar, a vaccine to protect against the pneumococcus bacteria, a leading cause of meningitis in infants and toddlers. Meningitis isn't very common, but it kills several hundred children each year and leaves others with brain damage and other neurological problems such as deafness and learning disabilities. A panel of advisers to the Centers for Disease Control and Prevention recommends that the vaccine become part of the routine immunization schedule. According to the AAP , your child needs all of the following vaccinations to stay healthy. Also note the age-appropriate immunization schedule recommended by the academy.