Many of us have not experienced deadly or crippling diseases like measles, rubella and polio. These diseases are mostly gone now that children receive immunizations starting at birth.

Have you ever wondered how pediatricians know what vaccines your child should have and when?

Your pediatrician follows the Recommended Immunization Schedule for Children and Adolescents. The schedule is carefully reviewed, updated and approved each year by the American Academy of Pediatrics, the Centers for Disease Control and Prevention, and the American Academy of Family Physicians.

Following are answers to common questions about how vaccines keep children safe from illnesses that we now only read about in history books.

Q: How are the timing and spacing of shots determined?

A: Scientists study what age a child’s immune system will provide the most effective protection after receiving a vaccine. They also look at when infants, children and adolescents are at most risk for each disease.

Q: Why are three or more doses of some vaccines needed?

A: It depends on how long a vaccine provides protection. Some need to be given three or four times. They are spaced out over a period that gives children the best protection.

Q: Can shots be spread out over a longer period?

A: This would leave a child unprotected for a longer time. Young babies are more likely to get very sick from vaccine-preventable diseases. Vaccinating them as soon as possible following the recommended schedule works best with the child’s immune system.

Spreading out the shots has not been scientifically shown to be safer. There is no research to show that children have the same protection with a very different schedule.

Q: Does it overwhelm a child’s immune system to give multiple shots in one visit?

A: No. Infants and children are exposed to more germs every day just by playing, eating and breathing than what is in any combination of vaccines on the schedule.

Q: Where can I find the recommended immunization schedule?

A: Find a chart of vaccines and diseases they prevent at http://bit.ly/IzSched18.

Excerpted from HealthyChildren.org,http://bit.ly/WhyIzSchedHC. Learn about 14 diseases that are history, thanks to vaccines at http://bit.ly/14diseasesHC.