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Children's Vaccines Health Center

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Vaccines: A Safe Choice

Are vaccines tested and monitored for safety?

Yes. Before vaccines are licensed, the FDA requires they be extensively tested to ensure safety. This process can take 10 years or longer. Once a vaccine is in use, the CDC and FDA monitor its side effects through the Vaccine Adverse Event Reporting System (VAERS). Any hint of a problem with a vaccine prompts further investigations by the CDC and FDA. If researchers find a vaccine may be causing a side effect, the CDC and FDA will initiate actions appropriate to the nature of the problem. This may include the changing of vaccine labels or packaging, distributing safety alerts, inspecting manufacturers' facilities and records, withdrawing recommendations for the use of the vaccine, or revoking the vaccine's license. For more information about VAERS, visit or call the toll-free VAERS information line at 1-800-822-7967.

For a quick reference sheet on key vaccine safety elements, an explanation of VAERS, and "what happens when rare, adverse events are detected?", consult the Surveillance and Vaccine Safety fact sheet.

Who should not be vaccinated?

Some people should not get certain vaccines or should wait to get them. For instance, children with compromised immune systems, as occurs with cancer patients, often need to wait to be vaccinated. Similarly, if a person has had a severe allergic reaction to a vaccine, she or he should not receive another dose. However, a person with a mild, common illness, such as a cold with a low-grade fever, does not have to wait to be vaccinated. Ask your health care provider for more information.

What should be done if someone has a reaction to a vaccine?

  • Call a doctor. If the person is having a severe reaction get him or her to a doctor right away.
  • After any reaction, tell your doctor what happened, the date and time it happened, and when the vaccination was given.
  • Ask your doctor, nurse, or health department to file a VAERS form, or call VAERS yourself at 1-800-822-7967.

Tell me more.

Please call our CDC National Immunization Information Hot Line at any time. Also, explore other areas of this immunization website ( for the most current and reliable information on vaccine safety.

CDC National Immunization Information Hot Line
English: 800-232-2522
Espaol: 800-232-0233

Visit these web sites for vaccine safety information and general information about vaccines:

Immunization Action Coalition (IAC) at
National Network for Immunization Information (NNii) at
Children's Hospital of Philadelphia Vaccine Education Center at

WebMD Public Information from the U.S. Department of Health and Human Services

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