Under recommended conditions, all vaccines used in national immunization programmes are safe and effective if used correctly. In practice, however, no vaccine is completely risk-free and adverse events can occasionally result after an immunization.
Adverse events can range from minor side-effects to more severe reactions. They can be a cause of public concerns about vaccine safety. To understand a specific event and to be able to respond appropriately, there are several questions that you need to answer:
■ What caused the reaction?
■ Was it related to the vaccine, or the way it was administered, or was it unrelated?
■ Are the reactions minor or severe?
Classification of AEFIs
AEFIs are grouped into five categories.
1.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.
2.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 vaccine leads to cases of paralytic polio.
3.Immunization error-related reaction
An AEFI that is caused by inappropriate vaccine handling, prescribing or administration and thus by its nature
Example: Transmission of infection by contaminated multi-dose vial.
4.Immunization anxiety-related reaction
An AEFI arising from anxiety about the immunization.
Example: Vasovagal syncope 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 association) but is in fact caused by malaria. Coincidental events reect the natural occurrence of health problems in the community with common problems being frequently reported.
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
■ is a congenital anomaly/birth defect, or
■ requires intervention to prevent permanent impairment or damage
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).
1.Vaccine product-related reaction & 2.Vaccine quality defect-related reaction
A vaccine reaction is an individual’s response to the inherent properties of the vaccine, even when the vaccine has been prepared, handled and administered correctly. From the 5 causes for AEFI from the previous page, vaccine reactions comprise vaccine product-related reactions and vaccine quality defect-related reactions.
Vaccine reactions can be classified into two groups:
A. Minor reactions Severe reactions
■ Usually occur within a few hours of injection.
■ Resolve after short period of time and pose little danger.
■ Local (includes pain, swelling or redness at the site of injection).
B. Systemic (includes fever, malaise, muscle pain, headache or loss of appetite).
■ Usually do not result in long-term problems.
■ Can be disabling.
■ Are rarely life threatening
■ Include seizures and allergic reactions caused by the body’s reaction to a particular component in a vaccine.
Severe vaccine reactions
Severe vaccine reactions include among others seizures, thrombocytopenia, hypotonic hyporesponsive episodes (HHE) and prolonged crying, which all need to be reported. Most severe vaccine reactions do not lead to long-term problems. Anaphylaxis, while potentially fatal, is treatable without leaving any longterm effects.
The difference between serious and severe adverse events
3.Immunization error-related reaction
Immunization errors often constitute the greatest proportion of AEFIs. They can include deaths associated with the reconstitution of vaccines with an incorrect diluent or a drug (e.g. insulin).
4.Immunization anxiety-related reactions
Individuals can react in anticipation to and as a result of an injection of any kind. These reactions are not related to the vaccine, but to fear of the injection. There are four reactions you may encounter.
Coincidental events occur after a vaccination has been given but are not caused by the vaccine or its administration. Vaccinations are normally scheduled in infancy and
early childhood, when illnesses are common and congenital or early neurological conditions become apparent. Coincidental events are inevitable when vaccinating children in these age groups, especially during a mass campaign. Applying the normal incidence of disease and death in these age groups along with the coverage and timing of immunizations allows estimation of the expected numbers of coincidental events after immunization. Estimates from the WHO Regional Office for the Western Pacific are presented in the table. For example, in Australia, each year there are likely to be 11 coincidental infant deaths the day after immunization.
Which of the following AEFIs would be classified as a ‘severe reaction’?
Select one or more:
❒ A. Vomiting, 5 minutes after receiving a BCG vaccination.
❒ B. Fainting, 5 minutes after receiving a DTP vaccination.
❒ C. Anaphylaxis, 5 minutes after receiving an Influenza-A vaccination.
❒ D. Febrile seizures, 4 days after a measles vaccination.
❒ E. Loss of appetite, 4 days after BCG vaccination.
Which of the following onset intervals of severe adverse events following immunization is probably not due to the given vaccine? Select one or more:
❒ A. Vaccine-associated paralytic poliomyelitis (VAPP) occurring 4–30 days after OPV.
❒ B. Febrile seizures occurring 6–12 days following measles vaccination.
❒ C. Thrombocytopenia occurring 15–35 days after measles vaccine.
❒ D. Anaphylaxis occuring 2–3 days after MMR vaccination.
❒ E. Prolonged crying for 0–24 hours after DTP vaccination.
Answer Question 1
Answers C and D are correct.
Minor reactions usually occur within a few hours of injection, resolve after a short period of time and pose little danger. These reactions are often local (including pain, swelling or redness at the site of injection) or systemic (including fever, malaise, muscle pain, headache or loss of appetite).
Severe reactions usually do not result in long-term problems, but can be disabling and, rarely, life threatening. These include, for example, seizures and allergic reactions caused by the body’s reaction to a particular component in a vaccine.
Answer Question 2
Answer D is incorrect.
Anaphylaxis has an onset interval of up to 1 hour following vaccination.
Dr. Vivek Jain