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Children's Vaccines Health Center

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Immunizations and Vaccines

What About Immunization Side Effects?

Today, vaccines are considered safe. As with any medication, they can have side effects. In most cases these are usually mild. Most common minor reactions to an immunization are:

  • Soreness or redness around the injection site
  • Low-grade fever

Side effects like these usually disappear in a few days. In extremely rare instances a high fever, in excess of 104 F, can occur with a vaccine. Fevers like this will not harm your children, but they can make them uncomfortable and upset.

Children have also been known to have serious allergic reactions to a vaccine. These usually happen very soon after getting the vaccine, and doctors' offices are well equipped to handle such reactions. If you think your child has or may have an allergy to any component in a vaccine, be sure to share that information with your doctor.

Medical providers agree that the proven preventive benefits of vaccines far outweigh the risks of the minimal side effects associated with them. More information about vaccine side effects and precautions can be found in the CDC's brochure Parents Guide to Childhood Immunizations.

How Effective Are Immunizations?

Vaccines are very effective at preventing disease, but they don't work all the time. Most of the recommended childhood immunizations are 90%-100% effective, according to the CDC.

However, for reasons that are not completely understood, sometimes a child will not become fully immunized against a disease after receiving a vaccine. This is all the more reason to get children vaccinated. Children in whom the vaccine is 100% effective protect those few who have not been completely immunized -- lessening everyone's chance of exposure to the disease.

Even in cases where a vaccine has not given your child 100% immunity, the symptoms -- if your child is exposed to an infectious disease -- will still usually be milder than if he or she had not been immunized at all.

Vaccine Myths and Misinformation

Here are important answers to three common misconceptions about vaccines.

Misconception #1: "We don't need to vaccinate against rare diseases."

Few parents today have even heard of all of the diseases we vaccinate against, let alone seen a case of the measles, diphtheria, or whooping cough.

This leads some to ask, "Why am I giving my child a vaccine against a disease that doesn't even exist?"

The answer is that it's the vaccines that keep these diseases so rare. Avoiding having your child immunized because of myths and misinformation about vaccine safety puts your child -- and public -- at risk. In communities where vaccine rates have dropped, these infectious diseases have quickly returned.

Misconception #2: "The preservative thimerosal makes vaccines risky."

Another concern about vaccines involves the use of a mercury-based preservative called thimerosal.

Thimerosal has been used as a preserving agent in some vaccines and other products since the 1930s. According to the CDC, no harmful effects have been reported from the amount of thimerosal used in vaccines, other than expected minor reactions like redness and swelling at the injection site.

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