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Childhood Vaccinations


Michael J. Smith

, MD, MSCE, Duke University

Last full review/revision Jul 2020| Content last modified Jul 2020
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Topic Resources

Children should be vaccinated to protect them against infectious diseases. Vaccines contain either noninfectious fragments of bacteria or viruses or whole forms of these organisms that have been weakened so that they do not cause disease. Giving a vaccine (usually by injection) stimulates the body's immune system to defend against that disease. Vaccination produces a state of immunity to disease and is thus sometimes termed immunization (see also Overview of Immunization).

Vaccine Effectiveness

Vaccines have eliminated smallpox and have nearly eliminated other infections, such as polio, that were once common childhood scourges in the United States. Despite this success, it is important for health care practitioners to continue to vaccinate children. Many of the diseases prevented by vaccination are still present in the United States and remain common in other parts of the world. For example, in 2019, there were 1,282 cases of measles, mostly in unvaccinated people. This is the greatest number of measles cases in the United States since 1992. These diseases can spread rapidly among unvaccinated children, who, because of the ease of modern travel, can be exposed even if they live in areas where a disease is not common.


How Many Cases of a Disease Can Be Prevented by Vaccines?


Before the Vaccine Was Developed*

Cases Reported in 2017 or 2016† ‡



Haemophilus influenzae type b infection (in children under 5 years)

20,000 (estimated)


117,333 (estimated)

An estimated 4,000†

Hepatitis B (acute)

66,232 (estimated)

An estimated 20,900†





Pertussis (whooping cough)



Pneumococcal infections that are severe—in all age groups

63,067 (estimated)

An estimated 30,400†

Pneumococcal infections that are severe—in children under 5 years

16,069 (estimated)

An estimated 1,700†

Polio that causes paralysis



Rotavirus infections that required hospitalization—in children under 3 years

62,500 (estimated)

An estimated 30,625†







Varicella (chickenpox)

4,085,120 (estimated)

An estimated 102,128†

* The average number of cases in the United States each year during the 20th century.

† These numbers are from 2016.

‡ The number of cases reported in the United States.

Adapted from Appendix E: Data and statistics: Impact of vaccines in the 20th and 21st centuries. In Epidemiology and Prevention of Vaccine-Preventable Diseases: The Pink Book, edited by Hamborsky J, Kroger A, and Wolfe S. Centers for Disease Control and Prevention, Washington D.C. Public Health Foundation, 2015, p. E-5. Available at the Centers for Disease Control and Prevention.

Vaccine Safety

No vaccine is 100% effective and 100% safe. A few vaccinated children do not become immune, and a few develop side effects. Most often, the side effects are minor, such as pain at the injection site, a rash, or a mild fever. Very rarely, there are more serious problems.

Vaccines are continuously undergoing improvements to ensure safety and effectiveness. Improvements include the use of

  • Acellular pertussis vaccine (typically combined with diphtheria and tetanus vaccine—DTaP), which has a much lower chance of causing side effects than the previously used whole-cell pertussis vaccine (also combined with diphtheria, and tetanus—DPT)

  • An inactivated, injectable polio vaccine instead of the previously used oral polio vaccine

The oral polio vaccine, which is made of a live, weakened virus, can cause polio if the weakened virus mutates, which happens once in every 2.4 million children. Although this risk is extremely low, it has led doctors in the United States to completely switch to the injectable polio vaccine.

Vaccine Adverse Event Reporting System (VAERS)

Before a new vaccine can be licensed, it, like any medical product, is tested in controlled clinical trials. Such trials compare the new vaccine to a placebo or to a previously existing vaccine for the same disease. Such trials show whether the vaccine is effective and identify common side effects. However, some side effects are too rare to be detected in any reasonably sized clinical trial and do not become apparent until after a vaccine is used routinely in many people. Thus, a surveillance system called the Vaccine Adverse Event Reporting System (see VAERS) was created to monitor the safety of vaccines that are used in the general public.

VAERS collects reports from people who believe that they had a side effect after a recent vaccination and from health care practitioners who identify certain possible side effects after a vaccine was given, even if they are unsure the effects are related to the vaccine. Thus, the existence of a VAERS report is not proof that a vaccine caused a certain side effect. VAERS is simply a system for collecting data about things that might be side effects. Then, the Food and Drug Administration (FDA) can further evaluate the concern by comparing how often the possible side effect occurred in people who were vaccinated to how often it occurred in people who were not vaccinated.

National Vaccine Injury Compensation Program

To help people evaluate the risks and benefits of vaccination, the federal government requires doctors to give parents a Vaccine Information Statement each time a child is vaccinated. Also, the National Vaccine Injury Compensation Program has been established to compensate people with proven vaccine-related injuries. This program was established because doctors and health authorities want as many children as possible to be protected from life-threatening diseases. When considering the risks and benefits of vaccination, parents must remember that the benefits of vaccination far outweigh the risks.

More Information about Childhood Vaccinations

The following are some English-language resources that may be useful. Please note that THE MANUAL is not responsible for the content of these resources.

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