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FAQ: Children's Vaccines

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What, exactly, are immunizations?

The idea that underlies immunizations is simple:

  1. Introduce a small part ("antigen") or a weakened live version of an infectious germ (like a bacterium or virus) into the body by injecting, swallowing, or inhaling it.
  2. This induces the body to make antibodies and other immunological defenses to fight off that perceived threat.
  3. Then, when exposed to the real infectious agent later on, the body has the pre-existing immunity to quickly recognize the germ and muster up the defenses to prevent it from invading and infecting the body.

Did You Know?

Under the Affordable Care Act, many health insurance plans will provide free children’s preventive care services, including checkups, vaccinations and screening tests. Learn more.

Health Insurance Center

What is a "live vaccine" vs. an "inactive vaccine"?

There are basically two ways to induce immunity against an infectious disease:

  1. Give a live but weakened version of the germ (as with vaccines to prevent against measles, mumps, rubella, chickenpox, and rotavirus).
  2. Introduce an inactive piece ("antigen") of the germ (as with vaccines to prevent against hepatitis A and B, diphtheria, tetanus, whooping cough, haemophilus, pneumococcus, meningococcus, human papilloma virus, and influenza), which then induces antibodies against the entire organism.

The live, weakened vaccines (called "attenuated") can actually cause a low-grade infection in the body. That's why, for example, a week or two following the chickenpox vaccine, your child may develop a slight rash and fever. It's a mild case of chickenpox - enough to induce immunity, but far less serious than the real infection.

Since they contain no live germs, the inactive vaccines do not cause an infection. However, as with any vaccine, there can be immediate, short-term side effects.

What are the potential side effects of vaccines and how often do they occur?

Any vaccine has the potential to cause side effects, and these vary from vaccine to vaccine. For specifics on each vaccine, see the CDC's web site:

Fortunately, such side effects are mild and short-lived. Your pediatric provider will give you a list of side effects to watch for after each immunization.

In general, most immunizations can cause:

  1. Pain and swelling at the injection site (usually occurs in less than 1 in 4 people, although more people may react toTdap)
  2. Itching at the injection site (usually in less than 1 in 20 people)
  3. Mild fever (under 102 F) (usually in less than 1 in 3 people)
  4. Moderate fever (102 F) (usually in less than 1 in 20 people)
  5. Generalized aches and pains

Severe side effects are very rare, so it is difficult to accurately assess how often they occur.

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