Vaccine Efficacy

**Definition:** A measurement of disease risk reduction among vaccinated compared to unvaccinated persons under ideal conditions such as in a clinical trial. Such disease reduction measured under typical field conditions is vaccine effectiveness. In contrast vaccine potency is measured in an assay to ensure proper dosing and storage of vaccines whereas vaccine immunogenicity measures its ability to induce an immune response in a vaccinated individual in observational studies.

**Tree numbers:** - E05.952.500