ADVERSE EVENTS FOLLOWING IMMUNIZATION (AEFI)
All vaccines are extremely, but not absolutely, safe and adverse reactions are rare but do occur after vaccinations. Definition: Adverse event following immunization (AEFI) is defined as quot;an untoward medical occurrence which follows immunization and which does not necessarily have a causal relationship with the usage of the vaccine.quot; This adverse event may be any unfavorable or unintended sign, an abnormal laboratory finding, a symptom or a disease.
Classification: AEFI are classified according to the probable cause, frequency and severity.
Causality-wise, AEFIs are classified according to probable cause, as follows:
• Vaccine-product related reaction, due to inherent property of the vaccine product/s, e.g. VAPP following OPV or febrile seizure following DTwP vaccination.
• Vaccine-quality defect related reaction, due to rare qualitative defect/s in the vaccine or its delivery device provided by manufacturer, e.g. insufficient inactivation of the constituent pathogen or contamination during manufacturing process.
• Immunization-errors related reaction (programmatic errors), due to inappropriate handling, prescribing or administration, e.g. injection abscess, sciatic nerve injury or toxic-shock syndrome due to contamination of vials.
• Immunization-anxiety related reactions, during or before the vaccination, e.g. syncope or breath-holding spell.
• Coincidental events, due to something other than the above factors with a chance temporal association. Considering the sheer number of children immunized, these events are inevitable which can be falsely attributed to immunization.
Frequency-wise AEFI are classified as: Very common (gt;10%), common (1-10%), uncommon (0.1-1.0%), rare (0.01-0.1%) and very rare (lt;0.01%).
Severity-wise these reactions are classified as:
• Minor vaccine reactions, which are very common and include local reactions, e.g.
pain swelling, redness, etc. at the injection site or systemic reactions, e.g. fever, irritability, malaise or others, e.g. rash after measles vaccine. These reactions may be due to the vaccineproduct or other excipients.• Severe AEFI are of minor medical significance but perceived to be severe in terms of intensity, e.g. high fever.
• Serious AEFI are potentially life-threatening, which may result in death, significant disability (including birth defects), hospitalization or require intervention to prevent permanent damage, e.g. anaphylaxis, seizures, intussusception, etc. AEFI, seen in clusters should also be considered as serious, due to adverse publicity and consequences on acceptance of immunization program.
Clinically, AEFRs may present immediately or after many days, with:
• Local reactions, e.g. pain, erythema and induration. These reactions are more common with DTwP and vaccines containing aluminum adjuvants. Frequency of local reactions tends to increase with subsequent doses. These reactions may be partly ameliorated by local ice packs application and paracetamol.
• Systemic reactions: Fever is the most common systemic reaction, more common with DTwP and vaccines containing aluminum-adjuvants. These reactions tend to decline with increasing number of doses. Although prophylactic paracetamol may reduce the incidence of post-vaccine febrile reactions, it has been found to blunt immune responses of some vaccines and should be used judiciously. Postvaccine fever rarely last for gt;48 hours and any fever persisting beyond this time should be evaluated for other causes.
• Allergic reactions are rare and may present with variable severity, ranging from mild urticaria to lifethreatening anaphylaxis. These reactions are rarely due to the vaccine antigen, usually caused by other vaccine constituents, e.g. residual animal protein (egg), stabilizers or preservatives (thiomersol). Since occurrence of anaphylaxis cannot be predicted in most cases vaccines, all vaccines should be observed for 15 minutes and patients with history of serious allergy to any of the vaccine constituents should not receive the vaccine.
Reporting: Any health care provider, whether in public or private sector, who comes across any AEFI, must report it to local health authorities, immediately in case of:
• Serious AEFI leading to death, disability, hospitalization or occur in clusters.
• Signal and events associated with a newly introduced vaccine;
• AEFI, probably due to immunization-error related reactions;
• Any other significant events of unexplained cause within 30 days of immunization.
Causality assessment: All reported AEFIs are investigated by specialists to: (a) ascertain diagnosis and availability of sufficient data for causality assessment, (b) objectively evaluate available facts of the case on the basis of a checklist, (c) assess the strength of association on the basis of an algorithm, and (d) classify the case, as follows:
• Consistent causal association to immunization, with further sub-classification as the reaction being: (A1) vaccine-product related, (A2) vaccine-quality related, (A3) immunization error and (A4) anxiety-related;
• Indeterminate, with further sub-classification as (B1) consistent temporal relationship but insufficient evidence, and (B2) conflicting qualifying factors;
• Inconsistent causal association to immunization or coincidental, and
• Unclassifiable.
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