Vaccine Safety > Issues of Interest > Multiple Vaccines
The Safety of Multiple Vaccines
Multiple Vaccines and the Immune System

1. How many vaccines does CDC recommend for children?
2. Why does CDC recommend that children receive so many shots?
3. Why are these vaccines given at such a young age? Wouldn’t it be safer to wait?
4. I’ve heard people talk about "simultaneous" and "combination" vaccines. What does this mean? Why are vaccines administered this way?
5. Is simultaneous vaccination with multiple vaccines safe? Wouldn’t it be safer to separate combination vaccines and spread them out, vaccinating against just one disease at a time?
6. Can so many vaccines, given so early in life, overwhelm a child’s immune system, suppressing it so it does not function correctly?
7. What research has been conducted to look at the possible link between vaccines and autoimmune diseases?

Related information:

• Institute of Medicine Report on Multiple Immunizations and Immune Dysfunction
• How Do Vaccines Protect Children from Diseases?

1. How many vaccines does CDC recommend for children?

Currently, CDC recommends vaccination against 12 vaccine preventable diseases. Because some of these vaccines have to be administered more than once, a child may receive up to 23 shots by the time he or she is 2 years of age. Depending on the timing, a child might receive up to six shots during one visit to the doctor.

2. Why does CDC recommend that children receive so many shots?

CDC recommends vaccination to protect children against 12 infectious diseases including measles, mumps, rubella (german measles), varicella (chickenpox), hepatitis B, diphtheria, tetanus, pertussis (whooping cough), Haemophilus influenzae type b (Hib), polio, influenza (flu), and pneumococcal disease. Vaccines are our best defense against these diseases which often result in serious complications such as pneumonia, meningitis (swelling of the lining of the brain), liver cancer, bloodstream infections, and even death.

3. Why are these vaccines given at such a young age? Wouldn’t it be safer to wait?

Children are given vaccines at a young age because this is when they are most vulnerable to certain diseases. Newborn babies are immune to some diseases because they have antibodies given to them from their mothers. However, this immunity only lasts about a year. Further, most young children do not have maternal immunity to diphtheria, whooping cough, polio, tetanus, hepatitis B, or Hib. If a child is not vaccinated and is exposed to a disease germ, the child’s body may not be strong enough to fight the disease.

An infant’s immune system is more than ready to respond to the very small number of weakened and killed antigens in vaccines. Babies have the capacity to respond to foreign antigens even before they are born. The human immune system has evolved since organisms began living on Earth and represents a culmination of the "best" of this experience. Just as babies are born with a full-length digestive system that simply stretches as the baby grows, they also are born with a well-developed immune system that can produce a variety of needed antibodies. However, infants lack the memory cells trained to defend against specific diseases. Because of this, they are particularly susceptible to diseases such as diphtheria, whooping cough, polio, tetanus, hepatitis B, and Hib. This is an important reason why the recommended childhood vaccination schedule begins so early – to prevent the diseases that children are susceptible to at such a young age.

4. I’ve heard people talk about "simultaneous" and "combination" vaccines. What does this mean? Why are vaccines administered this way?

"Simultaneous vaccination" is when multiple vaccines are administered during the same doctor’s visit, usually in separate limbs (e.g., one in each arm). A "combination vaccine" consists of two or more separate vaccines that have been combined into a single shot. Combination vaccines have been in use in the US since the mid-1940's. Examples of combination vaccines in current use are: DTaP (diphtheria-tetanus-pertussis), trivalent IPV (three strains of inactivated polio vaccine), MMR (measles-mumps-rubella), DTaP-Hib, and Hib-HepB (hepatitis B).

There are two practical factors in favor of giving a child several vaccinations during the same visit. First, we want to immunize children as quickly as possible to give them protection during the vulnerable early months of their lives. Second, giving several vaccinations at the same time will mean fewer office visits, which saves parents both time and money and may be less traumatic for the child.

5. Is simultaneous vaccination with multiple vaccines safe? Wouldn’t it be safer to separate combination vaccines and spread them out, vaccinating against just one disease at a time?

The available scientific data show that simultaneous vaccination with multiple vaccines has no adverse effect on the normal childhood immune system. A number of studies have been conducted to examine the effects of giving various combinations of vaccines simultaneously. These studies have shown that the recommended vaccines are as effective in combination as they are individually, and that such combinations carry no greater risk for adverse side effects. Consequently, both the Advisory Committee on Immunization Practices (ACIP) and the American Academy of Pediatrics (AAP) recommend simultaneous administration of all routine childhood vaccines when appropriate. Research is under way to find methods to combine more antigens in a single vaccine injection (for example, MMR and chickenpox). This will provide all the advantages of the individual vaccines, but will require fewer shots.

Another advantage is that combination vaccines result in fewer shots and less discomfort for children. In addition, spreading out the administration of separate vaccines may leave children unnecessarily vulnerable to disease.

6. Can so many vaccines, given so early in life, overwhelm a child’s immune system, suppressing it so it does not function correctly?

There is no evidence to suggest that the recommended childhood vaccines can "overload" the immune system. In contrast, from the moment babies are born, they are exposed to numerous bacteria and viruses on a daily basis. Eating food introduces new bacteria into the body, numerous bacteria live in the mouth and nose, and an infant places his/her hands or other objects in his/her mouth hundreds of times every hour, exposing the immune system to still more antigens. An upper respiratory viral infection exposes a child to 4 - 10 antigens, and a case of "strep throat" to 25 - 50. According to Adverse Events Associated with Childhood Vaccines, a 1994 report from the Institute of Medicine, "In the face of these normal events, it seems unlikely that the number of separate antigens contained in childhood vaccines . . . would represent an appreciable added burden on the immune system that would be immunosuppressive." Vaccines given in the first two years of life have been described as "a raindrop in the ocean of what infant's immune systems successfully encounter in their environment every day" (Vaccine Education Center, Children’s Hospital of Philadelphia, http://www.vaccine.chop.edu/concerns.shtml#question4)

7. What research has been conducted to look at the possible link between vaccines and autoimmune diseases?

The CDC takes concerns about vaccines and immune system dysfunction very seriously. Researchers at CDC and elsewhere have conducted studies to examine the possible link between vaccines and autoimmune conditions like multiple sclerosis (MS), diabetes, and asthma. These studies have been reassuring, providing evidence against a link between vaccines and autoimmune conditions. However, data has suggested a link between vaccines and other conditions. For example, recent studies suggest that alopecia (hair loss) may rarely occur in persons who have received hepatitis B vaccine. While the mechanisms responsible for alopecia following vaccination are not certain, it could be immune-mediated. Thus, CDC continues to conduct research to examine the effects vaccines may have on the immune system. In addition, CDC and the National Institutes of Health (NIH) asked the Institute of Medicine (IOM) to establish an independent expert committee to review hypotheses about existing immunization safety concerns. On November 12, 2001 the Immunization Safety Review Committee held an open scientific meeting to discuss the possible association between multiple immunizations in newborns and infants and immune system dysfunction.

The IOM report and the news release are available on the Web at:

• http://National-Academies.org
• http://www.iom.edu/imsafety   

Tortora GJ, Anagnostakos NP. Principles of Anatomy and Physiology, 3^rd ed. Harper and Row Publishers, New York, 1981.

Whitney EN, Hamilton EMN, Rolfes SR. Understanding Nutrition, 5^th ed. West Publishing Company, St. Paul, Minn., 1990.

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This page last modified on May 7, 2004