Adverse events following immunisation (AEFIs)

adverse events following immunisation (AEFIs)

Majority of adverse events following immunisation (AEFIs) are mild and resolve quickly although one cannot predict individuals who might have a mild or serious reaction to a vaccine (1).

AEFIs may be:

• true adverse reactions that are intrinsic to the vaccine
• caused by the way it is administered
• related to an underlying condition in the recipient
• coincidental - would have occurred regardless of the vaccine (1)

The WHO classifies AEFIs into four main categories:

• programme-related
• vaccine-induced
• coincidental
• unknown (1)

programme-related AEFIs

Programme-related AEFIs are seen as a result of inappropriate practices in the provision of vaccination. These may include:

• wrong dose of vaccine administered
• vaccines used beyond expiry date
• vaccines used at inappropriate intervals
• inappropriate route, site or technique of administration
• vaccine reconstituted with incorrect diluents
• wrong amount of diluent used
• vaccine prepared incorrectly
• mixing into inappropriate combinations
• drugs substituted for vaccine or diluents
• vaccine or diluent contaminated
• vaccine or diluent stored incorrectly
• contraindications not elicited or ignored
• reconstituted vaccine kept beyond the recommended period (1)

In some cases administration of the vaccine may result in AEFI rather than components of the vaccine itself e.g. - fainting in older children and adults during the 1999–2000 meningitis C immunisation campaign (1).

vaccine-induced AEFIs

Caused by either a particular vaccine or its component parts. These may be:

• induced, direct effects of the vaccine or one of its components e.g - local reactions and fever within 48 hours of DTaP/IPV/Hib, rash and fever seven to ten days after MMR, and parotitis three weeks after MMR
• due to an underlying medical condition e.g - vaccineassociated paralysis which very rarely followed the use of live attenuated oral polio vaccine in a child with previously unrecognised severe combined immune deficiency
• idiosyncratic response e.g. - idiopathic thrombocytopaenic purpura (ITP) within 30 days of MMR, and anaphylaxis immediately after vaccination, also includes medical conditions that would have occurred at some point in an individual but are triggered earlier by the vaccination. This may include febrile seizures in a child with a family history of the same, or onset of infantile spasms (1).

common vaccine-induced AEFIs

Common vaccine-induced AEFIs include:

• pain, swelling or redness at the site of injection
  • occurs commonly after immunisation and should be anticipated
  • local adverse reactions that generally start within a few hours of the injection and are usually mild and self-limiting
  • although these are often referred to as ‘hypersensitivity reactions’, they are not allergic in origin, but may be either due to high titres of antibody or a direct effect of the vaccine product, e.g. endotoxin in whole-cell bacterial vaccines
  • the occurrence or severity of such local reactions does not contraindicate further doses of immunisation with the same vaccine or vaccines containing the same antigens
• systemic adverse reactions which include fever, malaise, myalgia¸ irritability, headache and loss of appetite
  • the timing of systemic reactions will vary according to the characteristics of the vaccine received, the age of the recipient and the biological response to that vaccine. For example, fever may start within a few hours of tetanus containing vaccines but occurs seven to ten days after measles containing vaccine
  • The occurrence of such systemic reactions does not contraindicate further doses of the same vaccine or vaccines containing the same antigens

managing common vaccine induced AEFIs

Patients should be educated about the AEFIs and how such events should be managed (1).

• fever over 37.5 C
  • common in children and are usually mild
  • paracetamol or ibuprofen liquid to treat a fever should be given at the time of immunisation
    • although paracetamol or ibuprofen reduce the duration and distress associated with fever, there is no evidence that they prevent febrile convulsions
    • therefore routine use therefore to prevent fever following vaccination is not recommended since there is some evidence that prophylactic administration of antipyretic drugs around the time of vaccination may lower antibody responses to some vaccines
  • aspirin, or medicines that contain aspirin should never be given to children under 16 years old because of the risk of developing Reye’s syndrome
• local rations
  • usually self limiting
  • paracetamol or ibuprofen can be given if it results in any discomfort

Reference:

• (1) Immunisation Against Infectious Disease - "The Green Book". Chapter 8. Vaccine safety and adverse events following immunisation (April 2019)