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.
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.
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.
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.
An AEFI arising from anxiety about the immunization.
Example: Vasovagal syncopeVasovagal syncopeA neurovascular reaction that leads to fainting. in an adolescent during/following vaccination.
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.
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.|
Answers A and D are correct.
- An AEFI is any adverse eventAdverse event following immunization (AEFI)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. observed following immunization. Some may be due to the vaccine, some due to error in the administration of the vaccine, and some are the result of unrelated coincidence.
- An adverse vaccine reactionVaccine reaction (also referred to as adverse vaccine reaction or adverse reaction)A classification of AEFI referring to events caused or precipitated by the vaccine when given correctly, caused by the inherent properties of the vaccine. is a subset of AEFI. It refers to a vaccine-related event caused or precipitated by a vaccine when given correctly. Note that the rate of adverse vaccine reactions is very much lower than the rate of health-damaging complications resulting from the disease in unvaccinated individuals.
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.