Vaccine Adverse Event Reporting System

The Vaccine Adverse Event Reporting System (VAERS) is a national passive surveillance system that is co-managed by the U.S. Centers for Disease Control and Prevention (CDC) and the U.S. Food and Drug Administration (FDA). VAERS monitors the safety of all vaccines licensed for use in the United States. VAERS accepts reports from healthcare providers, manufacturers, and the public of adverse events following immunization. VAERS serves as an early warning system that can detect patterns in adverse event reports and determine whether further investigation is necessary. Serious and other selected reports are reviewed by medical staff and epidemiologists at both CDC and FDA. However, VAERS data alone are usually not sufficient to determine if a vaccine caused an adverse event. An adverse event is considered serious if it is life threatening, or results in death, a persistent or significant disability or incapacity, congenital anomaly or birth defect, hospitalization, or prolongation of existing hospitalization.

Reporting to VAERS

Healthcare providers are encouraged to submit adverse events they think are clinically important and are required by federal law to report certain adverse events after vaccination; a report may be filed even if the provider is not sure if the vaccine caused an adverse event. VAERS does not actively solicit reports in any systematic way from all people who have been vaccinated. Reports can be submitted by anyone, including healthcare providers, patients, or family members.

Accessing VAERS Data

VAERS reports are available through the public CDC's website, WONDER. All personal identifying information is removed prior to posting the public data. VAERS data in WONDER should be used with caution because it only contains the original VAERS report information and does not reflect data collected during follow-up. Events reported to VAERS and viewed in WONDER should not be considered as evidence that the vaccine caused the event.

Limitations of VAERS

Some adverse events reported to VAERS may have occurred by chance following vaccination, while others may actually be caused by vaccination. However, VAERS data alone cannot usually determine causality. Underreporting and biased reporting are main limitations, inherent to passive surveillance systems, and therefore VAERS only receives reports for only a small percentage of actual events in the general population. VAERS reports can also vary in quality and completeness. A report to VAERS generally does not conclude that a vaccine caused an adverse event. It only confirms that the adverse event happened sometime after a vaccine was received. If a patient believes they have a serious adverse event following a vaccination, they should seek help from their healthcare provider.