Overview
- An adverse event (AE) is any medical event occurring after vaccination, regardless of whether it is causally related.
- A side effect is a medical event that is confirmed to be caused by a vaccine or medical intervention.
- Distinguishing an AE from a side effect requires formal causality assessment based on biological plausibility, timing, specificity, and clinical evidence.
- Absolute safety can never be proven due to β-error in observational studies; therefore, safety is defined through accumulated evidence.
- A vaccine’s safety profile is established through pre-licensure clinical trials and continuous post-licensure surveillance, supported by benefit–risk assessment.
