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The Vaccine Adverse Events Reporting System (VAERS) is an early warning system that allows health care providers, vaccine manufacturers and the general public to report health concerns (adverse events) after vaccination. Established in 1990, VAERS can monitor for increases in known vaccination side effects, such as a sore arm or shortness of breath. It also helps scientists detect patterns and identify rare adverse events after vaccination. With the COVID-19 vaccinations, for example, VAERS has helped identify adverse events such as severe allergic reactions or myocarditis.

A report to VAERS does not mean a vaccine caused the adverse event.

Researchers cannot use the number of times an adverse event is reported in VAERS to determine how common that adverse event is. Instead, researchers identify patterns to determine if an adverse event happens more often after vaccination than in the general population. Only then can researchers know if there is a connection between vaccination and an adverse event.

What to know about VAERS:

• It’s a nationwide program.
• Anyone can report vaccination side effects or adverse events to VAERS.
• It helps identify rare adverse events related to vaccinations.
• Health care providers and vaccine manufacturers are required by law to report certain events after vaccination.
• If a pattern of events following vaccination is detected, follow-up studies can determine whether the adverse event occurs more often after vaccination than it does in the general population. Follow-up studies can also determine if vaccination is a cause of the adverse event.

The data collected and studied through VAERS comes from a significant sample size. The sample size is often much larger than what is available through clinical trials or state data. Given how rare some serious adverse events are, a larger sample size gives scientists a much better chance of determining if  vaccination caused an adverse event.

Vaccine clinical trials include participants in a “control group” who receive a placebo (a dose that contains no vaccine). Some people in this group will report complications to their health. If participants who received the vaccine report a complication more often than those in the control group, there could be a connection between the vaccine and the complication.

VAERS does not compare how often reported events occur after vaccination to how often they occur in the general population. Reports in VAERS must be investigated before any conclusions can be made. Once a pattern is identified using VAERS, scientists may use a control group to determine if an adverse event occurs more often after vaccination than it does for the general population.

During the COVID-19 pandemic there has been a lot of false information claiming reports in VAERS are definitive evidence of side effects from the COVID-19 vaccination. In fact, VAERS is an early warning system that provides patterns for researchers to investigate. Reports of vaccination side effects or adverse events in VAERS do not mean they were caused by vaccination.