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Immunology 101 Series: Do Too Many Vaccines Too Soon Overwhelm the Immune System?

By Aimee Pugh-Bernard, PhD

In the sixth installment of the Immunology 101 Series, Aimee will explain why the immunization schedule begins at precisely the right time (i.e. starting just after birth) and does not overwhelm the immune system.

Have you ever taken your child to the pediatrician’s office and questioned the number of immunizations recommended per visit?  Maybe you’re concerned that your infant’s immune system is not yet ready to train against a variety of pathogens or that too many vaccines will overwhelm your child’s immune system. Whatever your concerns might be, read on to find out the scientific facts and answers from Aimee.

Are Vaccines Given Too Soon? Are Too Many Vaccines Given at One Time?

Although you may never have thought about it, babies are immediately and continually exposed to pathogens from the moment they enter the world. Starting at birth, babies come into contact with millions of pathogens every day. Dr. Paul Offit (Chief of Infectious Diseases and the Director of the Vaccine Education Center at the Children’s Hospital of Philadelphia and my personal immunization super hero) states that, “When you look at what’s in vaccines and the number of immunological components in vaccines, it really is literally a drop in the ocean of what we encounter and manage every day.” In real numbers, the total number of immunological components in the vaccines that are currently recommended to protect against 14 diseases is slightly less than 160 compared to the millions (1,000,000s!) of pathogens we encounter every day by simply eating, breathing, and living our lives. I agree, that sounds like a ‘drop in the ocean’ to me!

To answer the same question from a basic science perspective, I have one more piece of important information to tell you – not every immune cell responds to each pathogen. The immune cells (you know, the specialized cells called B and T cells you may have read about  in ‘Understanding the Immune System’) in our bodies are actually each specific for different pathogens, actually different pieces of different pathogens. The combination of all the immune cells in each of our bodies results in a tremendously large collection of cells that can combat any pathogen that comes our way. If you take this a step further, this means that for every pathogen introduced into our body, whether in a vaccine or through exposure in everyday life, only a handful of specific immune cells will actually respond. This bit of immunological knowledge should help seal the deal on any concerns you may have regarding overwhelming the immune system with vaccines. The immune system has evolved to combat hundreds to millions of pathogens at the same time by division of labor. Simple as that, some cells respond to each pathogen while others rest but remain alert while waiting for their specific pathogen to enter.

What About Alternative Schedules?

You may have heard about alternative immunization schedules from friends or via the internet. It may sound appealing to purchase a book or follow a “custom” schedule that provides a “compromise” to the CDC and AAP-recommended immunization schedule, but it’s important to know that these alternative schedules are not based in science nor have they been tested and reviewed for safety.  The current immunization schedule is recommended by the Centers for Disease Control (CDC), the American Academy of Pediatricians (AAP), and the American Academy of Family Physicians (AAFP). The people who represent these groups are professionals trained in medicine and science. They have painstakingly reviewed piles of data from every single vaccine trial and have given their approval with the knowledge that numerous years of rigorous testing have deemed the vaccines we now see on the immunization schedule as safe and effective. These experts determine each vaccine’s dose timing using two factors. First, it is scheduled for the age when the body’s immune system will respond best. Second, it is balanced with the need to provide protection to infants and children at the earliest possible age.Quick Review_Too Many Too Soon

Attempting to recreate an altered immunization schedule for your child is not recommended. The experts created the recommended schedule because it yields the safest and most protective results for the health of your child, your family, and our community. They’ve done the work so you don’t have to!

It can be hard to tell what is true on the internet, and I urge you to take caution when researching topics that affect your family’s health on the internet. If you have questions about the immunization schedule, I encourage you to first speak to your child’s doctor. The following sites also provide helpful, fact-based information:

Centers for Disease Control and Prevention
The Children’s Hospital of Philadelphia Vaccine Education Center
American Academy of Pediatrics
Vaccinate Your Baby
Immunize for Good


Offit, PA et al. Addressing parents’ concerns: Do multiple vaccines overwhelm the immune or weaken the infant’s immune system? Pediatrics. 2002; 109(1):124-129

Offit, PA and Moser, CA. Vaccines and Your Child: Separating fact from Fiction. New York: Columbia University Press; 2011.

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