Vaccine Adverse Event Reporting System (VAERS) is a passive reporting system, meaning that reports about adverse events are not automatically collected, but require a report to be filed to VAERS. VAERS reports can be submitted voluntarily by anyone, including healthcare providers, patients, or family members. Reports vary in quality and completeness. They often lack details and sometimes can have information that contains errors. About 85-90% of vaccine adverse event reports concern relatively minor events, such as fevers or redness and swelling at the injection site. The remaining reports (less than 15%) describe serious events, such as hospitalizations, life-threatening illnesses, or deaths. The reports of serious events are of greatest concern and receive the most careful scrutiny by VAERS staff. VAERS researchers apply procedures and methods of analysis to help them closely monitor the safety of vaccines. When a concern arises, action is taken. The hope is that this brief explanation of the factors associated with vaccines and adverse events will assist users in understanding the data they are viewing.
Vaccines protect many people from dangerous illnesses, but vaccines, like drugs, can cause side effects, a small percentage of which may be serious. VAERS is used to continually monitor reports to determine whether any vaccine or vaccine lot has a higher than expected rate of events.