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 to fulfill their duty as regulatory agencies charged with protecting the public. As it is based on submissions by the public, VAERS is susceptible to unverified reports, misattribution, underreporting, and inconsistent data quality. Raw, unverified data from VAERS has often been used by the anti-vaccine community to justify misinformation regarding the safety of vaccines; it is generally not possible to find out from VAERS data if a vaccine caused an adverse event, or how common the event might be. Origins 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. 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. Operation 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. 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. Use in research and litigation Many medical researchers make use of VAERS to study the effects of vaccination.