Skip Navigation

About the VAERS Program

Background and Public Health Importance

The Vaccine Adverse Event Reporting System (VAERS) is a national vaccine safety surveillance program co-sponsored by the Centers for Disease Control and Prevention (CDC) and the Food and Drug Administration (FDA). VAERS is a post-marketing safety surveillance program, collecting information about adverse events (possible side effects) that occur after the administration of vaccines licensed for use in the United States. 

The National Childhood Vaccine Injury Act (NCVIA) of 1986 requires health professionals and vaccine manufacturers to report to the U.S. Department of Health and Human Services specific adverse events that occur after the administration of routinely recommended vaccines. In response to NCVIA, CDC and FDA established the Vaccine Adverse Event Reporting System (VAERS) in 1990 (Chen, Vaccine, 1994).

VAERS has demonstrated its public health importance by providing health scientists with signals about possible adverse events following immunization. In one instance, VAERS detected reports for intussusception over that what would be expected to occur by chance alone after the RotaShield rotavirus vaccine in 1999. Epidemiologic studies confirmed an increased risk, and these data contributed to the product's removal from the US market. In another example, VAERS determined that there may be a potential for a small increase in risk for  Guillain-Barre syndrome after the meningococcal conjugate vaccine, Menactra. As a result of this finding, a history of Guillain-Barre syndrome became a contraindication to the vaccine and further controlled studies are currently underway to research this issue.

[top]

Number of Reports VAERS Receives 

VAERS receives around 30,000 reports annually, with 13% classified as serious (e.g., associated with disability, hospitalization, life-threatening illness or death) (CDC VAERS Master Search Tool, April 2, 2008). Since 1990, VAERS has received over 200,000 reports, most of which describe mild side effects such as fever. Very rarely, people experience serious adverse events following immunization. By monitoring such events, VAERS helps to identify any important new safety concerns and thereby assists in ensuring that the benefits of vaccines continue to be far greater than the risks.

Many different types of adverse events occur after vaccination. About 85-90% of the reports describe mild adverse events such as fever, local reactions, and episodes of crying or mild irritability. The remaining reports reflect serious adverse events involving life-threatening conditions, hospitalization, permanent disability, or death, which may or may not have been caused by a vaccine.

[top]

Objectives of VAERS 

The primary objectives of VAERS are to:

  1. Detect new, unusual, or rare vaccine adverse events (VAEs);
  2. Monitor increases in known adverse events;
  3. Identify potential patient risk factors for particular types of adverse events;
  4. Identify vaccine lots with increased numbers or types of reported adverse events; and
  5. Assess the safety of newly licensed vaccines. 

[top]

What Can Be Reported to VAERS?

VAERS seeks reports of any clinically significant medical event that occurs after vaccination, even if the reporter cannot be certain that the event was caused by the vaccine. CDC/ISO and FDA review adverse reports; VAERS has identified important signals that after further research resulted in changes to vaccine recommendations. VAERS encourages the reporting of any clinically significant adverse event that occurs after the administration of any vaccine licensed in the United States. You should report adverse events even if you are unsure whether a vaccine caused the event.

[top]

Who Reports to VAERS?

Anyone can file a VAERS report, including health care providers, manufacturers, and vaccine recipients. The majority of VAERS reports are sent in by vaccine manufacturers (37%) and health care providers (36%). The remaining reports are obtained from state immunization programs (10%), vaccine recipients (or their parent/guardians, 7%) and other sources (10%). Vaccine recipients or their parents or guardians are encouraged to seek the help of their health care professional in filling out the VAERS form. Each report provides valuable information that is added to the VAERS database. Accurate and complete reporting of post-vaccination events supplies the information needed for evaluation of vaccine safety. The CDC and FDA use VAERS information to ensure the safest strategies of vaccine use and to further reduce the rare risks associated with vaccines. 

[top]

Which Government Agencies Manage VAERS?

VAERS is a national passive reporting system co-managed 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.

[top]

VAERS Does Not Determine Causality  

Although VAERS can rarely provide definitive evidence of causal associations between vaccines and particular risks, its unique role as a national spontaneous reporting system enables the early detection of signals that can then be more rigorously investigated. VAERS receives reports of many events that occur after immunization. Some of these events may occur coincidentally following vaccination, while others may truly be caused by vaccination. Studies help determine if there is more than a temporal (time) association between immunization and adverse events. The fact that an adverse event occurred following immunization is not conclusive evidence that the event was caused by a vaccine. Factors such as medical history, diagnostic tests, and other medication given near the time of vaccination must be examined to help to determine the cause of adverse events.

[top]

The Main Limitations of VAERS Data

VAERS is subject to the limitations inherent in any passive surveillance system:

  1. Underreporting- Underreporting is common to all surveillance systems which require someone to complete and send a report.  However we also know that underreporting occurs more often with less serious adverse events and that more serious vaccine adverse event are more likely to be reported to VAERS.
  2. Differential reporting-meaning that reporting is increased in the first few years after vaccine licensure, or increased reporting of events occurring soon after vaccination
  3. Stimulated reporting -meaning that reporting increases after a known or alleged type of adverse event
  4. Reporting of coincidental events-Some of the reports in VAERS are coincidental to vaccination, meaning they would have occurred even if vaccination had not and they are not caused by vaccination.
  5. Data quality-Since reports are accepted from anyone, the data reported is not always complete or accurate.
  6. No denominator data-VAERS does not provide denominator data. In other words, it does not collect data on the number of doses of vaccines administered and does not allow for calculation of the actual rates of adverse events.

[top]

How are VAERS Reports Followed Up?

The CDC and FDA require additional information on selected VAERS reports for the public health purpose of helping to ensure the safety of U.S.-licensed vaccines. You or your health care provider may be contacted for follow-up information by VAERS staff after your report is received. These selected reports are followed up by a team of health care professionals to obtain additional information (such as medical records and autopsy reports) to provide as complete a picture of the case as possible. All records sent to VAERS are kept confidential as required by law. The patient's consent is not required to release the medical records to VAERS. If you have questions about how the Health Insurance Portability and Accountability Act of 1996 (HIPAA) applies to VAERS, please visit our VAERS Privacy Policies and Disclaimers section.

[top]

Does VAERS Provide General Vaccine Information?

No. VAERS only collects and analyzes adverse event reports. For general information about vaccine safety, visit CDC's Vaccine Safety Web site. For information about specific vaccines, immunization schedules, publications on vaccine-preventable diseases, and more, visit CDC's Vaccines and Immunizations Web site or call the CDC INFO Contact Center Information Line at (800) 232-4636. 

[top]

How to Obtain More Information About VAERS

You can get more information about VAERS by- 

[top]

Frequently Asked Questions (FAQs)

Visit our Frequently Asked Questions (FAQs) page.

 [top]