AEFI Causality Assessment
WHO Algorithm - Classify adverse events following immunization
Is there a valid diagnosis of an adverse event?
An adverse event is any untoward medical occurrence following immunization, which does not necessarily have a causal relationship with the vaccine.
WHO AEFI Classification Overview
Event caused by an inherent property of the vaccine. Known reaction consistent with product label/literature.
Event caused by a defect in the vaccine product (manufacturing, storage, handling).
Event caused by inappropriate handling, prescribing, or administration of the vaccine.
Event arising from anxiety about immunization (vasovagal, hyperventilation).
Temporal association is consistent but insufficient evidence to classify as A or C. Needs further investigation.
Insufficient information available to determine causality. Further information needed.
Event explained by another cause (underlying illness, medication, other exposure). Temporal but not causal.