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About VAERS

NEW! Expanded public access to VAERS data

On May 8, 2025, CDC and FDA expanded public access to VAERS data in the WONDER database (wonder.cdc.gov) and in VAERS downloadable files (vaers.hhs.gov) to provide a more complete picture of all reported adverse events following vaccination received. This enhancement is part of a broader CDC and FDA effort to improve transparency and access to vaccine safety data, while continuing to protect patient privacy.

  • Prior to May 8, VAERS public data sets only included the first submitted VAERS report (or primary report) for a patient, vaccine and dose combination.
  • VAERS public data sets now include all subsequent reports (or secondary reports) from the same or different reporters, for the same patient, vaccine, and dose combination.
  • Based on this enhancement, in the downloadable data file, it will appear that additional reports have been added, but these are actually the subsequent or secondary reports that have previously not been included in the public data sets.
  • It’s important to note these new reports are related to already reported events and do not represent additional reports of adverse events.

Background and Public Health Importance

Medical professionals working with vaccines

Established in 1990, the Vaccine Adverse Event Reporting System (VAERS) is a national early warning system to detect possible safety problems in U.S.-licensed vaccines. VAERS is co-managed by the Centers for Disease Control and Prevention (CDC) and the U.S. Food and Drug Administration (FDA). VAERS accepts and analyzes reports of adverse events (possible side effects) after a person has received a vaccination. Anyone can report an adverse event to VAERS. Healthcare professionals are required to report certain adverse events and vaccine manufacturers are required to report all adverse events that come to their attention.

VAERS is a passive reporting system, meaning it relies on individuals to send in reports of their experiences to CDC and FDA. VAERS is not designed to determine if a vaccine caused a health problem, but is especially useful for detecting unusual or unexpected patterns of adverse event reporting that might indicate a possible safety problem with a vaccine. This way, VAERS can provide CDC and FDA with valuable information that additional work and evaluation is necessary to further assess a possible safety concern.

Objectives of VAERS

The primary objectives of VAERS are to:

  • Detect new, unusual, or rare vaccine adverse events;
  • Monitor increases in known adverse events;
  • Identify potential patient risk factors for particular types of adverse events;
  • Assess the safety of newly licensed vaccines;
  • Determine and address possible reporting clusters (e.g., suspected localized [temporally or geographically] or product-/batch-/lot-specific adverse event reporting);
  • Recognize persistent safe-use problems and administration errors;
  • Provide a national safety monitoring system that extends to the entire general population for response to public health emergencies, such as a large-scale pandemic influenza vaccination program.

VAERS is co-sponsored by the Centers for Disease Control and Prevention (CDC), and the Food and Drug Administration (FDA), agencies of the U.S. Department of Health and Human Services (HHS).