Vaccine Adverse Event Reporting System

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The Vaccine Adverse Event Reporting System (VAERS) is a United States program for vaccine safety, co-managed by the U.S. Centers for Disease Control and Prevention (CDC) and the Food and Drug Administration (FDA). VAERS is a postmarketing surveillance program, collecting information about adverse events (possible harmful side effects) that occur after administration of vaccines to ascertain whether the risk–benefit ratio is high enough to justify continued use of any particular vaccine.

VAERS, the Vaccine Safety Datalink, and the Clinical Immunization Safety Assessment (CISA) Network are tools by which the CDC and FDA monitor vaccine safety[1] to fulfill their duty as regulatory agencies charged with protecting the public. VAERS has limitations, including unverified reports, misattribution, underreporting, and inconsistent data quality.[2]

CDC cautions that it is generally not possible to find out from VAERS data if a vaccine caused the adverse event, or how common the event might be.[3]


The program is an outgrowth of the 1986 National Childhood Vaccine Injury Act (NCVIA), which requires health care providers to report:

  • Any event listed by the vaccine manufacturer as a contraindication to subsequent doses of the vaccine.
  • Any event listed in the Reportable Events Table that occurs within the specified time period after vaccination. The data are stored electronically by the CDC in the Vaccine Safety Datalink (VSD).

VAERS was established in 1990 and is managed jointly by the FDA and the CDC.[4] It is meant to act as a sort of "early warning system"—a way for physicians and researchers to identify possible unforeseen reactions or side effects of vaccination for further study.


Higher-priority uses of the data include reports of death and other serious adverse events, recognizing and detecting adverse effects, and finding unexpected adverse events involving new vaccines. The VAERS data are also used to monitor known reactions to vaccines and for vaccine lot surveillance. Data mining techniques such as empirical Bayes methods can be used to improve the quality of data analysis.[4] The system was used in 1999 to identify a rotavirus vaccine that had an increased risk of a bowel obstruction condition, and confirmatory research led to the vaccine's use being suspended.[5][6][7]


Like other spontaneous reporting systems, VAERS has several limitations, including underreporting, unverified reports, inconsistent data quality, and inadequate data about the number of people vaccinated. Indeed, an autism activist named Jim Laidler once reported to VAERS that a vaccine had turned him into The Incredible Hulk. The report was accepted and entered into the database, but the dubious nature thereof prompted a VAERS representative to contact Mr. Laidler, who then gave his consent to delete the report.[8]

Use in research and litigation[edit]

Many medical researchers make use of VAERS to study the effects of vaccination. VAERS warns researchers using its database that the data should not be used in isolation to draw conclusions about cause and effect.[9] Nonetheless, data from VAERS has been used in vaccine litigation to support the claim that vaccines cause autism.

Litigation related to vaccines and autism has led to an increase in VAERS reports filed by plaintiff's attorneys. A 2006 article in Pediatrics found that most VAERS reports related to thimerosal, and many related to autism, were filed in connection with litigation, leading the authors to caution that inappropriate reliance on VAERS data may be a source of bias.[10] The study's lead author stated: "Lawyers are manipulating this system to show increases [in vaccine-related adverse events] that are based on litigation, not health research."[11] Paul Offit, chief of infectious disease at Children's Hospital of Philadelphia, wrote:

Public health officials were disappointed to learn that reports of autism to VAERS weren't coming from parents, doctors, nurses, or nurse practitioners; they were coming from personal-injury lawyers ... For the lawyers, VAERS reports hadn't been a self-fulfilling prophecy; they'd been a self-generated prophecy.[11]


Due to the program's open and accessible design and its allowance of unverified reports, incomplete VAERS data is often used in false claims regarding vaccine safety. The U.S. Centers for Disease Control has warned that data from VAERS is not enough to determine whether a vaccine can cause a particular adverse event.[12]

There has been a surge in reports to VAERS during the COVID-19 pandemic, which has led to the data being used in COVID-19 vaccine-related misinformation.[12] In fact, analytics of VAERS data using proportional reporting reveals that the vaccine is not associated with a higher risk of anaphylaxis,[13] autoimmune side effects[14] or neurological presentations.[15] VAERS data needs appropriate interpretation:

VAERS remains open to reports from individuals, allied healthcare workers and even unrelated third parties. In other words, while there is a risk of unreported AEFIs, there may also be a degree of over-reporting (the same AEFI, for instance, may be reported by the physician, the nurse and the patient as well, without the knowledge of any of the other parties). Moreover, VAERS does not verify the accuracy or veracity of reports, nor does it require a causal attribution. This is notably illustrated by the number of accidents, drownings and congenital diagnoses reported to VAERS, none of which could conceivably be a causal consequence of vaccination. Thus, VAERS data must be appropriately analysed to fulfill its function, which is to generate early potential safety signals rather than to substantiate a causal relationship.

— Chris von Csefalvay, VAERS data reveals no increased risk of neuroautoimmune adverse events from COVID-19 vaccines


  1. ^ Centers for Disease Control and Prevention, Vaccine Safety Monitoring at CDC, retrieved March 11, 2015.
  2. ^ Shimabukuro, TT; Nguyen, M; Martin, D; DeStefano, F (August 2015). "Safety monitoring in the Vaccine Adverse Event Reporting System (VAERS)". Vaccine. 33 (36): 4398–4405. doi:10.1016/j.vaccine.2015.07.035. PMC 4632204. PMID 26209838.
  3. ^ "Vaccine Adverse Event Reporting System (VAERS)". February 27, 2019. Retrieved December 6, 2019.
  4. ^ a b Woo EJ, Ball R, Burwen DR, Braun MM (2008). "Effects of stratification on data mining in the US Vaccine Adverse Event Reporting System (VAERS)". Drug Saf. 31 (8): 667–74. doi:10.2165/00002018-200831080-00003. PMID 18636785. S2CID 40587832.
  5. ^ "Intussusception Among Recipients of Rotavirus Vaccine -- United States, 1998-1999". Retrieved November 12, 2020.
  6. ^ "Vaccines: VPD-VAC/Rotavirus/Rotashield and Intussusception Historical info". April 15, 2019. Retrieved November 12, 2020.
  7. ^ Murphy, Trudy V.; Gargiullo, Paul M.; Massoudi, Mehran S.; Nelson, David B.; Jumaan, Aisha O.; Okoro, Catherine A.; Zanardi, Lynn R.; Setia, Sabeena; Fair, Elizabeth; LeBaron, Charles W.; Schwartz, Benjamin (February 22, 2001). "Intussusception among Infants Given an Oral Rotavirus Vaccine". New England Journal of Medicine. 344 (8): 564–572. doi:10.1056/NEJM200102223440804. ISSN 0028-4793. PMID 11207352.
  8. ^ Hall, Harriet (2018). "Diving into the VAERS Dumpster: Fake News about Vaccine Injuries". Skeptical Inquirer. 42 (6): 28–31.
  9. ^ "VAERS Data". VAERS.
  10. ^ Goodman MJ, Nordin J (2006). "Vaccine adverse event reporting system reporting source: a possible source of bias in longitudinal studies". Pediatrics. 117 (2): 387–90. doi:10.1542/peds.2004-2687. PMID 16452357. S2CID 36547618.
  11. ^ a b Offit, Paul A. (2008). Autism's False Prophets: Bad Science, Risky Medicine, and the Search for a Cure. New York: Columbia University Press. ISBN 978-0-231-14636-4.
  12. ^ a b Gabrielle Settles (May 3, 2021). "Federal VAERS database is a critical tool for researchers, but a breeding ground for misinformation". PolitiFact.
  13. ^ "Allergic Reactions Including Anaphylaxis After Receipt of the First Dose of Moderna COVID-19 Vaccine — United States, December 21, 2020–January 10, 2021". Morbidity and Mortality Weekly Report. 70 (4): 125–129. January 29, 2021. doi:10.15585/mmwr.mm7004e1. ISSN 0149-2195. PMC 7842812. PMID 33507892.
  14. ^ Csefalvay, Chris von (July 7, 2021). "A case-control study of autoimmune AEFIs following COVID-19 vaccination reported to VAERS". medRxiv: 2021.07.06.21260074. doi:10.1101/2021.07.06.21260074.
  15. ^ Csefalvay, Chris von (June 17, 2021). "VAERS data reveals no increased risk of neuroautoimmune adverse events from COVID-19 vaccines". medRxiv: 2021.06.13.21258851. doi:10.1101/2021.06.13.21258851.

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