Adverse events: Classification

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. AEFIs are divided in 5 categories. Click on each heading to learn more about the 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.

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.

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.

Example: Transmission of infection by contaminated multidose vial.

Immunization anxiety-related reaction

An AEFI arising from anxiety about the immunization.

Example: Vasovagal syncopeVasovagal syncopeA neurovascular reaction that leads to fainting. in an adolescent during/following vaccination.

Coincidental event

An AEFI that is caused by something other than the vaccine product, immunization error or immunization anxiety.

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.