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Safety & Prevention

Child Immunization Schedule: Why Is It Like That?

infant getting vaccinated infant getting vaccinated

​Q1: Who decides what immunizations children need?

A: Each year, top disease experts and doctors who care for children work together to decide which vaccines to recommend that will best protect U.S. children from diseases. The schedule is evaluated each year based on the most recent scientific data available. Changes are announced in January, if needed. The schedule is approved by the American Academy of Pediatrics, the Centers for Disease Control and Prevention, and the American Academy of Family Physicians.

Q2: How are the timing and spacing of the shots determined?

A: The timing for each dose of a vaccine is based on 2 factors. First, scientists determine the age when the body’s immune system will provide optimal protection after vaccination. Second, that information is balanced with the need to provide protection to infants, children and adolescents at the earliest possible time based on the highest age of risk for that disease. 

Q3: Why do some vaccines need 3 or more doses?

A: Researchers are always studying how long a vaccine will provide protection. For some vaccines three or four doses are needed to fully protect your child. The doses need to be spaced out a specific amount of time to work best.

Q4: Why is there only one recommended schedule for all children? Are there some children who shouldn’t receive some vaccines?

A: Your child’s health and safety are very important to your child’s doctor. The schedule is considered the ideal schedule for healthy children but rarely, there may be exceptions.

For example, your child might not receive certain vaccines if she has a weakened immune system due to a chronic condition like leukemia or is taking certain medicines that weaken the immune system. Sometimes a shot needs to be delayed for a short time, and sometimes not given at all. Your pediatrician stays updated about any changes to the immunization schedule. This is one reason your child’s complete medical history is taken at the pediatrician’s office.

Q5: Can the shots be spread out over a longer period of time?

A: First, you would not want your child to go unprotected that long. Of all age groups, young babies are hospitalized and die more often from the diseases we are trying to prevent with vaccines, so it is important to vaccinate them as soon as possible. Second, the recommended schedule is designed to work best with a child’s immune system at certain ages and at specific time intervals between doses. There is no research to show that a child would be equally protected against diseases with a very different schedule. Also, there is no scientific reason why spreading out the shots would be safer. But we do know that any length of time without immunizations is a time without protection against vaccine preventable diseases.

Q6: I’ve seen another schedule that allows the shots to be spread out. Can I follow that schedule if my child would still be vaccinated in time for school?

A: There is no scientific basis for such “alternative” schedules. No one knows how well they would work to protect your child from diseases. And if many parents in any community decided to follow an alternative schedule, diseases will be able to spread much more quickly. Also, people who are too sick or too young to receive vaccines are placed at risk when they are around unvaccinated children.

For example, following one nonstandard schedule would leave children without full polio protection until age 4. Yet it would take only one case of polio to be brought into the U.S. for the disease to take hold again in this country. These alternative schedules also often delay the measles vaccine until age 3 or later. We have already seen outbreaks of measles in some parts of the country because children were not immunized. This is a highly infectious disease that can cause serious harm--even death. The reason we recommend vaccines when we do is because young children are more vulnerable to these diseases.

Pediatricians want parents to have reliable, complete, and science-based information, so that they can make the best decision for their child about vaccination. Unfortunately, there are a few pediatricians in the country who go against the existing science, often for personal gain, such as selling books, or advertisements on their websites. The overwhelming majority of pediatricians in the US strongly recommend following the recommended schedule.

Q7: Is it possible that my child has natural immunity to one or more of these diseases? If so, can we skip the shots?

A: Tests that check for immunity to certain diseases do not work well in young children. The best way to know that children are protected is to immunize them.

Q8: Does it overwhelm a child’s immune system to give multiple shots in one visit?

A: Infants and children are exposed to many germs every day just by playing, eating, and breathing. Their immune systems fight those germs, also called antigens, to keep the body healthy. The amount of antigens that children fight every day (2,000-6,000) is much more than the antigens in any combination of vaccines on the current schedule​. So children’s immune systems are not overwhelmed by vaccines.

Q9: There are no shots given at 9 months, other than maybe influenza vaccine or catch-up vaccines. Could we give some shots at that visit instead of at 6 months or 12 months?

A: Waiting until 9 months would leave the child unprotected from some diseases, but 9 months is too early for some of the 12-18 month vaccines. For example, it is too early for the live measles, mumps, rubella and varicella vaccines, since some infants might have a bit of protection left from their mother during the pregnancy, and that protection could make the vaccine less effective.

Additional Information:

Last Updated
American Academy of Pediatrics (Copyright © 2018)
The information contained on this Web site should not be used as a substitute for the medical care and advice of your pediatrician. There may be variations in treatment that your pediatrician may recommend based on individual facts and circumstances.
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