The National Childhood Vaccine Injury Act of 1986 (42 U.S.C. §§ 300aa-1 to 300aa-34) set up a federal vaccine injury compensation program as well as included legal requirements for vaccine providers to report serious health problems following vaccination to the federal Vaccine Adverse Events Reporting System (VAERS).
From HHS website:
VAERS is a passive reporting system, meaning it relies on individuals to send in reports of their experiences. Anyone can submit a report to VAERS, including parents and patients.
Healthcare providers are required by law to report to VAERS:
Any adverse event listed in the VAERS Table of Reportable Events Following Vaccination that occurs within the specified time period after vaccinations
An adverse event listed by the vaccine manufacturer as a contraindication to further doses of the vaccine
Healthcare providers are strongly encouraged to report to VAERS:
Any adverse event that occurs after the administration of a vaccine licensed in the United States, whether it is or is not clear that a vaccine caused the adverse event
Vaccine administration errors
Vaccine manufacturers are required to report to VAERS all adverse events that come to their attention.
Online reporting is strongly encouraged. Please report clinically important adverse events that occur after vaccination of adults and children, even if you are not sure whether the vaccine caused the adverse event.