The Vaccine Adverse Event Reporting System is a United States program for vaccine safety, co-managed 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 administration of vaccines. VAERS has several limitations, including unverified reports, underreporting, inconsistent data quality, and absence of an unvaccinated control group.