Classification of AEFIs

Although all vaccines used in NIPs are safe and effective if used correctly, no vaccine is completely risk-free and adverse events will occasionally result after an immunization.

An adverse event following immunization (AEFI) is any untoward medical occurrence which follows immunization and which does not necessarily have a causal relationship with the usage of the vaccine. The adverse event may be any unfavourable or unintended sign, abnormal laboratory finding, symptom or disease.

AEFIs are grouped into five categories.

Vaccine product-related reaction

An AEFI that is caused or precipitated by a vaccine due to one or more of the inherent properties of the vaccine product.

Example: extensive limb swelling following DTP vaccination, aseptic meningitis following mump vaccine.

Vaccine quality defect-related reaction

An AEFI that is caused or precipitated by a vaccine that is due to one or more quality defects of the vaccine product including its administration device as provided by the manufacturer. Quality defect is defined as any deviation of the vaccine product as manufactured from its set quality specifications.

Example: Failure by the manufacturer to completely inactivate a lot of inactivated polio vaccineInactivated polio vaccine (IPV)An inactivated (killed) polio vaccine, developed in 1955 by Dr. Jonas Salk. Unlike oral polio vaccine (OPV), a LAV vaccine, IPV must be injected to produce the desired immune response. leads to cases of paralytic polio.

Immunization error-related reaction

An AEFI that is caused by inappropriate vaccine handling, prescribing or administration and thus by its nature is preventable. Inappropriate usage is defined as the usage other than what is authorized and recommended in a given jurisdiction based on scientific evidence or expert recommendation.

Example: Transmission of infection by contaminated multidose vial.

Immunization anxiety-related reaction

An AEFI arising from anxiety about the immunization. The term “immunization anxiety-related reaction” is used to describe a range of symptoms and signs that may arise from anxiety about immunization and include vasovagal-mediated reactions, hyperventilation-mediated reactions and stress-related psychiatric reactions or disorders. The term “anxiety” does not, however, adequately cover the presentation of all these AEFI and anxiety may not manifest during such events. Thus, a new term is proposed that better describes this cause-specific AEFI, which is “immunization stress-related response (ISRR)".

Example: Syncope or hyperventilation.

Coincidental event

An AEFI that is caused by something other than the vaccine product, immunization error or immunization anxiety, but where a temporal association with immunization exists.

Example: A fever occurs at the time of the vaccination (temporal associationTemporal associationTwo or more events that occur around the same time. The preceding event may or may not be Two or more events that occur around the same time. The preceding event may or may not be causally related to the later one.) but is in fact caused by malariaMalariaAn infectious disease caused by a parasite (plasmodium) that is transmitted from human to human by the bite of infected female Anopheles mosquitoes. Malaria is a leading cause of morbidity and mortality in sub-Saharan Africa..

Coincidental events reflect the natural occurrence of health problems in the community with common problems being frequently reported.

Serious event

Seriousness is based on patient/event outcome or action criteria and defines regulatory reporting obligations. An AEFI will be considered serious if:

  • it results in death;
  • is life-threatening;
  • requires in-patient hospitalization or prolongation of existing hospitalization;
  • results in persistent or significant disability/incapacity, or
  • is a congenital anomaly/birth defect.

The ICH E2A and E2D guidelines also state that other situations, such as other important medical events that may jeopardize the patient or may require intervention to prevent one of the outcomes above, should also be considered serious after applying medical and scientific judgment. Those “other situations” are open to interpretation and could vary from jurisdiction to jurisdiction.104

Event severity

Severe is used to describe the intensity of a specific event (as in mild, moderate or severe); the event itself, however, may be of relatively minor medical significance (e.g. fever is a common relatively minor medical event, but according to its severity it can be graded as mild fever or moderate fever).

Key point

It is important to note that ‘serious’ and ‘severe’ are often used as interchangeable terms but they are not.


True or false?

An anaphylactic reaction following immunization that results in the death of the patient is considered a serious event.


This statement is true.

  • Events that are life-threatening or result in the death of a patient are defined as "serious".