Each person is unique and may react differently to immunization.

• Occasionally, people who receive a vaccine do not respond to it and may still get the illness the vaccine was meant to protect them against.
• In most cases, vaccines are effective and cause no side effects, or only mild reactions such as fever or soreness at the injection site.
• Very rarely, people experience more serious side effects, like allergic reactions. Be sure to tell your health care provider if you have health problems or known allergies to medications or food.
• Severe reactions to vaccines occur so rarely that the risk is difficult to calculate.

The Centers for Disease Control and Prevention (CDC) and the Food and Drug Administration (FDA) continually work to make already safe vaccines even safer. In the rare event that a child is injured by a vaccine, he or she may be compensated through the National Vaccine Injury Compensation Program (VICP). For more information about VICP visit http://bhpr.hrsa.gov/vicp/ or call 1-800-338-2382.

Not vaccinating your child? Be aware of the risks.
Immunizations, like any medication, can cause side effects. However, a decision not to immunize a child also involves risk. It is a decision to put the child and others who come into contact with him or her at risk of contracting a disease that could be dangerous or deadly. Consider measles. One out of 30 children with measles gets pneumonia. For every 1,000 children who get the disease, one or two will die from it. Thanks to vaccines, we have few cases of measles in the U.S. today. However, the disease is extremely contagious and each year dozens of cases are imported from abroad into the U.S., threatening the health of people who have not been vaccinated and those for whom the vaccine was not effective. Unvaccinated children are also at risk from meningitis (swelling of the lining of the brain) caused by Hib (a severe bacterial infection), bloodstream infections caused by pneumococcus, deafness caused by mumps, and liver cancer caused by hepatitis B virus.

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 www.vaers.org 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?",.

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 (http://www.cdc.gov/nip) for the most current and reliable information on vaccine safety.

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

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

• Immunization Action Coalition (IAC) at http://www.immunize.org/
• National Network for Immunization Information (NNii) at http://www.immunizationinfo.org/
• Children's Hospital of Philadelphia Vaccine Education Center at http://www.vaccine.chop.edu/index/shtml