A U.S. passive surveillance system operated jointly by the CDC and FDA that collects reports of adverse health events following vaccination from healthcare providers and the public.
The Vaccine Adverse Event Reporting System (VAERS) is a passive surveillance database established in 1990 by the Centers for Disease Control and Prevention (CDC) and the Food and Drug Administration (FDA) to monitor vaccine safety. The system accepts reports from healthcare providers, manufacturers, and the general public regarding adverse events occurring after vaccination. VAERS data is publicly accessible through the CDC website, though the system explicitly notes that reports do not prove causation—a reported event may be temporal coincidence rather than vaccine-related injury.
VAERS operates with known limitations that health officials have documented for decades. The system's passive nature means it captures only a fraction of actual adverse events, as reporting is voluntary and depends on awareness and willingness to file reports. Studies have estimated underreporting rates of 90 percent or higher for mild to moderate events. During the COVID-19 vaccination campaign (2021-2022), VAERS received unprecedented public attention, with millions accessing the database. The system recorded over 1.3 million reports by mid-2023, though the CDC emphasized that investigations into specific serious outcomes (myocarditis, thrombosis) determined that vaccines posed lower risks than the diseases they prevented. Researchers and regulators continue to cite VAERS as one component of post-market vaccine surveillance, alongside more rigorous systems like the Vaccine Safety Datalink and Clinical Immunization Safety Assessment Project.
