Adverse Events Following Immunisation
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Direct answer
An adverse event following immunisation is any untoward medical occurrence that follows vaccination but need not have a causal relationship to it — the definition's second half is the whole point, because coincidence, programme error and vaccine reaction all surface as "AEFI". India's surveillance classifies causes into vaccine product-related reactions, immunisation error-related reactions (too cold, wrong site, wrong dose, unsafe injection), coincidental events, and immunisation anxiety-related reactions such as faints and hysteria; serious AEFIs — death, hospitalisation, disability, cluster events — must be reported within 24 hours and investigated by district and national AEFI committees. Most AEFIs are expected, mild and self-limiting: fever, local pain and swelling after DPT, or the characteristic axillary adenitis after BCG.
What you must remember
- Definition to quote: any untoward medical occurrence which follows immunisation and which does not necessarily have a causal relationship with the vaccine — causality is established later, not assumed at reporting.
- Cause classification (current national guidelines): vaccine product-related reaction; vaccine quality defect-related reaction; immunisation error-related reaction; immunisation anxiety-related reaction; coincidental event.- Common expected reactions: fever and local induration after DPT-containing vaccines (the whole-cell pertussis component is the irritant); axillary lymphadenitis and local pustule after BCG; fever and rash about a week after MR vaccines.
- Programme errors to list: wrong site or route (BCG must be intradermal over the left deltoid — subcutaneous BCG causes abscess), reconstitution errors, frozen DPT or hepatitis B (shake test), and unsafe injection practice.
- Serious AEFI triggers for same-day reporting: death, hospitalisation, significant disability, cluster of similar events, or an event previously unreported nationally.
- Anaphylaxis management: every session site must have adrenaline 1:1000 at 0.01 mL/kg (up to 0.5 mL) intramuscular in the anterolateral thigh, with the child kept supine and observed; steroids and antihistamines are adjuncts, not first-line.
- System structure in India: reporting by ANM or medical officer into the AEFI surveillance stream; the district AEFI committee does preliminary causality assessment and the national committee classifies serious cases.
Managing a collapse at a session site
A nine-month-old screams, goes limp and develops urticaria within ten minutes of MR vaccine at an anganwadi session. The sequence that saves him is drilled: supine position with legs raised, adrenaline 1:1000, 0.1 mL for his roughly 10 kg (0.01 mL/kg) intramuscularly in the thigh, repeat at five to fifteen minutes if shock persists, airway watch, urgent referral — and documentation as a serious AEFI with reporting within 24 hours. The vaccine vial is retained, the batch number recorded, the session site inventoried for cold-chain breach or reconstitution error, and the district committee begins causality assessment while parents are counselled from a position of honesty: a probable rare anaphylaxis to a vaccine component is very different from programme error, and the investigation determines which.
The counterfactual matters as much as the event. Measles itself kills and disables at rates thousands of times higher than any vaccine reaction; the anxiety-faint cluster sweeping a school vaccination line is managed by quiet removal, privacy and reassurance, not adrenaline. Distinguishing anaphylaxis (rapid, urticaria, airway and circulatory signs) from syncope (pallor, brief, resolves flat) at a session site is precisely the practical skill viva examiners now test.
Where students slip
Candidates confuse an adverse event with an adverse reaction — every reaction is an event, but most events prove coincidental, and the definition's "does not necessarily have a causal relationship" clause is the standard one-mark discriminator. They misattribute the fever timeline: DPT fever peaks within 48 hours, MR fever and rash arrive around days 5 to 12, and mixing the two suggests infection rather than reaction. They forget the BCG-specific facts — 0.05 mL intradermal left deltoid, axillary (not cervical-first) adenitis as its classic reaction, and its persistence months after vaccination. On management, the lethal slip is reaching for hydrocortisone first; adrenaline intramuscular in the thigh is first-line, and steroids only adjunct. Finally, examiners ask which events qualify as serious (death, hospitalisation, disability, clusters) and the reporting clock — 24 hours for serious AEFIs.
Frequently asked questions
What is an adverse event following immunisation?
Any untoward medical occurrence after vaccination that does not necessarily have a causal relationship with the vaccine or its process — causality is determined by investigation, not by timing alone.
How are AEFIs classified by cause?
Vaccine product-related, vaccine quality defect-related, immunisation error-related, immunisation anxiety-related reactions, and coincidental events that merely followed vaccination.
Which AEFI must be reported within 24 hours?
Serious events — death, life-threatening illness, hospitalisation, significant disability, congenital anomaly, and cluster events — triggering district and national committee investigation.
How is anaphylaxis after vaccination managed?
Immediate adrenaline 1:1000 at 0.01 mL/kg (maximum 0.5 mL) intramuscularly in the anterolateral thigh, supine positioning, airway support and referral, with doses repeated if shock persists; steroids are adjuncts only.
Why does BCG cause axillary lymphadenitis?
Intradermal BCG in the left deltoid drains to the ipsilateral axillary nodes, so a local ulcer and axillary adenitis are expected, usually self-limiting vaccine product-related reactions.