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U.S. Department of Health and Human Services

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What is the Vaccine Adverse Event Reporting System (VAERS)?

The Vaccine Adverse Event Reporting System (VAERS) is used by FDA and the Centers for Disease Control and Prevention to

  • detect new, unusual or rare vaccine side effects (adverse events)
  • monitor increases in known adverse events
  • identify potential risk factors for particular types of adverse events
  • identify vaccine lots with increased numbers or types of reported adverse events
  • assess the safety of newly licensed vaccines

VAERS receives reports of many events that occur after vaccination. A report of an event to VAERS does not mean a vaccine caused the event. Some of these events may occur coincidentally during the time period following vaccination, while others may actually be caused by vaccination. When FDA reviews VAERS data, the agency looks for patterns of adverse events that may possibly be linked to a vaccine. Such patterns may need to be studied further.

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