4.1 Definition and Categorization of AEFI

• Adverse event following immunization (AEFI) is any untoward medical occurrence which:
• Follows immunization.
• Does not necessarily have a causal relationship with the usage of the vaccine.
• May be any unfavorable or unintended sign, abnormal laboratory finding, symptom or disease.
• Can either be true adverse events - i.e., resulting from the vaccine or immunization process - or coincidental events that are not due to the vaccine or immunization process but are temporarily associated with immunization.