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. The adverse event may be any unfavorable or unintended sign, abnormal laboratory finding, symptom or disease. Surveillance of AEFIs aims to monitor vaccine and immunization program safety and to detect population-specific, rare, late-onset or unexpected adverse events that may not be detected in pre-licensure vaccine trials.

Adverse events following Immunization .

  • Minor AEFI

Usually occur within a few hours of injection, resolve after short period of time and pose little danger.

Local signs includes pain, swelling or redness at the site of injection; systemic signs include fever, malaise, muscle pain, headache or loss of appetite.

  • Severe AEFI

Usually do not result in long-term problems, can be disabling and are rarely life threatening. They include seizures and allergic reactions caused by the body’s reaction to a particular component in a vaccine.


  • Minor Vaccine reactions

Ideally vaccines will cause no, or only minor (i.e. non-severe) adverse reactions. Vaccination induces immunity by causing the recipient’s immune system to react to antigens contained in the vaccine. Local and systemic reactions such as pain or fever can occur as part of the immune response. In addition, other vaccine components (e.g. adjuvants, stabilizers, and preservatives) can trigger reactions. A successful vaccine keeps even minor reactions to a minimum while producing the best possible immune response. These reactions typically occur within a day or two of immunization

  • Severe vaccine reactions

Severe vaccine reactions include among others seizures, thrombocytopenia, hypotonic hypo responsive episodes (HHE) and prolonged crying, which all need to be reported. Most severe vaccine reactions do not lead to long-term problems.

  • 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.

  • 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


  • Immunization error-related reaction

An AEFI that is caused by inappropriate vaccine handling, prescribing or administration and thus by its nature is preventable.

  • Immunization anxiety-related reaction

An AEFI arising from anxiety about the immunization

  • Coincidental event

An AEFI that is caused by something other than the vaccine


Parents should be given advice about AEFIs that they can expect and how such events should be managed. Fevers over 37.5˚C are common in children and are usually mild. Advice on the use and appropriate dose of paracetamol or ibuprofen liquid to prevent or treat a fever should be given at the time of immunization. Local reactions are usually self-limiting and do not require treatment. If they appear to cause discomfort, then paracetamol or ibuprofen can be given.


Pharmacovigilance is the practice of detecting, assessing, understanding, responding and preventing adverse drug reactions, including reactions to vaccines. It is an integral part of the regulation of drug and vaccine safety. Surveillance systems exist at national and international levels to ensure effective monitoring and prompt actions in response to AEFIs.

  • Anaphylaxis, while potentially fatal, is treatable without leaving any long term effects.
  • Persistent or significant disability/incapacity,