A safety signal is any trend, pattern, set of symptoms or other indicator that a drug or intervention may have an adverse event that requires more examination. Some surveillance systems are specifically set up for the purpose of looking for safety signals, such as the Vaccine Adverse Event Reporting System. If a significant number of people report the same adverse event after administration of the same vaccine, that’s a signal that may require additional research to understand. Safety signals can be known or previously unknown adverse events or side effects.
