VAERS accepts reports of adverse events and reactions that occur following vaccination. Healthcare providers, vaccine manufacturers,
and the public can submit reports to VAERS. While very important in monitoring vaccine safety, VAERS reports alone cannot be used to
determine if a vaccine caused or contributed to an adverse event or illness. The reports may contain information that is incomplete,
inaccurate, coincidental, or unverifiable. Most reports to VAERS are voluntary, which means they are subject to biases. This creates
specific limitations on how the data can be used scientifically. Data from VAERS reports should always be interpreted with these
limitations in mind.
The strengths of VAERS are that it is national in scope and can quickly provide an early warning of a safety problem with a vaccine.
As part of CDC and FDA's multi-system approach to post-licensure vaccine safety monitoring, VAERS is designed to rapidly detect
unusual or unexpected patterns of adverse events, also known as "safety signals." If a safety signal is found in VAERS, further
studies can be done in safety systems such as the CDC's Vaccine Safety Datalink (VSD) or the Clinical Immunization Safety
Assessment (CISA) project. These systems do not have the same limitations as VAERS, and can better assess health risks and
possible connections between adverse events and a vaccine.
Key considerations and limitations of VAERS data:
Vaccine providers are encouraged to report any clinically significant health problem following vaccination to VAERS,
whether or not they believe the vaccine was the cause.
Reports may include incomplete, inaccurate, coincidental and unverified information.
The number of reports alone cannot be interpreted or used to reach conclusions about the existence, severity, frequency,
or rates of problems associated with vaccines.
VAERS data are limited to vaccine adverse event reports received between 1990 and the most recent date for which data are available.
VAERS data do not represent all known safety information for a vaccine and should be interpreted in the context of other
VAERS data available to the public include only the initial report data to VAERS. Updated data which contains data from medical records
and corrections reported during follow up are used by the government for analysis. However, for numerous reasons including data consistency,
these amended data are not available to the public.