Reactogenicity

In clinical trials, the term reactogenicity refers to the property of a vaccine of being able to produce common, "expected" adverse reactions, especially excessive immunological responses and associated signs and symptoms, including fever and sore arm at the injection site. Other manifestations of reactogenicity typically identified in such trials include bruising, redness, induration, and swelling.
Origin.
The term reactogenicity was coined by the US Food and Drug Administration (FDA). Typically, reactogenicity is observed upon the administration of an adjuvant, which is a chemical additive intended for enhancing the recipient's immune response to the antigen that is present in a vaccine but can also be observed in non-adjuvanted vaccines. Reactogenicity describes the immediate short-term reactions of a system to vaccines and should not be confused with the long-term consequences sequelae. Assessments of reactogenicity are carried out to evaluate the safety and usability of an experimental vaccine (see Investigational New Drug). It is unclear whether a higher degree of reactogenicity to a vaccine correlates with more severe adverse events, which would require hospitalization or are life-threatening. Adverse events have been linked to a higher degree of reactogenicity; however, the links might have been coincidental. After assessing large databases relating to these events for many years, the FDA has not been able to make such a correlation.
Definition.
The US National Institutes of Health (NIH) has provided the following definition of reactogenicity: