Adverse events

Classification and definition

An adverse event following immunization (AEFIAEFIAny 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. AEFI is used in accordance with "Definition and Application of Terms for Vaccine Pharmacovilance", a report of CIOMS/WHO, working group on Vaccine Pharmacovigilance.) 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 can be related to the vaccine itself (product or quality defect-related reactions), to the vaccination process (error or stress related reactions) or can occur independently from vaccination (coincidental).

Click on the appropriate section below to read more.

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.

Question

It is important to understand the different meanings of an adverse event following immunization (or AEFI) and an adverse vaccine reaction. Can you tell the difference? Select the right answers:

A. An adverse vaccine reaction is a vaccine-related event caused or precipitated by a vaccine when given correctly.
B. An adverse vaccine reaction can be caused by errors in the administration of the vaccine.
C. An adverse vaccine reaction can be the result of unrelated coincidence.
D. An adverse event following immunization can be due to all of the causes stated in A, B, and C.

Answer

Answers A and D are correct.

Key point

The difference between a reaction related to the vaccine and an adverse event which can have other causes should be explained to patients and parents. This ensures that they have all information they need to make an informed decision about receiving an immunization for themselves or their children.

Trusted and well-informed health care providers are best suited to provide such information. Information about the immunization(s) should be provided well ahead of the immunization visit. This gives parents the time to understand the information well and ask questions that will increase their trust.