# Adverse Events Following Immunisation

> Adverse events following immunisation for NEET-PG Paediatrics, covering AEFI categories, WHO causality assessment, reporting and vaccine contraindications.

- Canonical URL: https://prepelephant.com/topics/neet-pg/paediatrics/adverse-events-following-immunisation
- Exam / course: NEET-PG · Subject: Paediatrics
- Publisher: PrepElephant (https://prepelephant.com) — Prepared and reviewed by the PrepElephant Academic Review Team
- First published: 2026-10-15
- Last updated: 2026-10-15
- Reference basis: Nelson Textbook of Pediatrics; IAP Guidebook on Immunization; WHO Global Manual on Surveillance of Adverse Events Following Immunization
- How to cite: "Adverse Events Following Immunisation", PrepElephant, https://prepelephant.com/topics/neet-pg/paediatrics/adverse-events-following-immunisation

## Direct answer

Adverse events following immunisation (AEFI) are any untoward medical occurrences that follow a vaccine dose, whether or not the vaccine actually caused them. Each event is classified by its cause, given a causality category, and reported through district surveillance so that serious events receive a full investigation.

## What you must remember

- **Definition:** an AEFI is any untoward medical event after immunisation, and the term does not by itself imply that the vaccine caused it.
- **Five categories:** vaccine product-related reaction, vaccine quality defect-related reaction, immunisation error-related reaction, immunisation anxiety-related reaction and coincidental event.
- **Causality categories:** consistent, inconsistent, indeterminate or unclassifiable, as set out in the WHO framework.
- **Immunisation error:** a wrong vaccine, dose, diluent, route or site, which is preventable and therefore worth reporting.
- **Contraindication:** a severe allergic reaction, such as anaphylaxis, after a previous dose or a vaccine component means that vaccine must not be repeated.
- **Precaution:** moderate or severe acute illness is a reason to defer vaccination, whereas mild illness with low-grade fever is not.
- **Observation:** vaccinees are watched for a short period after injection, commonly 15 to 30 minutes, so that immediate reactions can be treated.
- **Serious AEFI:** death, hospitalisation or disability needs prompt reporting and investigation by the AEFI committee.

## Working up one AEFI report, step by step

A 15-month-old develops a febrile convulsion the evening after a DTwP dose. The investigating team works through a fixed sequence rather than deciding from timing alone.

1. **Report the event.** The health worker records the vaccine name, batch number, dose, route, site and time of onset. Missing batch data makes the later causality assessment much harder.
2. **Verify the immunisation.** Check that the right vaccine, dose and diluent were used and that the cold chain was maintained.
3. **Review the clinical picture.** Look at the time to onset, the child's history and any alternative cause, such as a viral infection with fever.
4. **Assign the category.** Decide whether the event is a product, quality, error, anxiety or coincidental reaction.
5. **Assess causality.** Apply the WHO causality category, which may be indeterminate if the evidence is incomplete.
6. **Act and feed back.** Treat the child, record the outcome and share lessons with the programme so that similar events are prevented.

An incomplete first step often leaves the whole case unclassifiable, so the quality of the initial record matters most.

## Where the exam tries to catch you

Most AEFI questions turn on one of three misreadings.

- **Trap:** taking timing as proof that the vaccine caused the event — **Correct:** temporal association alone does not establish causality, so the event stays an AEFI until it is assessed.
- **Trap:** treating a mild fever as a contraindication — **Correct:** mild illness is not a contraindication, whereas a severe allergic reaction to the same vaccine is.
- **Trap:** dismissing an immunisation error as not an AEFI — **Correct:** errors are a formal AEFI category, and they are reported because they are preventable.

## Frequently asked questions

### Which AEFI category covers a wrong diluent or a vaccine given by the wrong route?

A wrong diluent, dose, route or site is classed as an immunisation error-related reaction. Such events are preventable, so they are reported and used for training rather than attributed to the vaccine product.

### What separates a vaccine product-related reaction from a coincidental event?

A vaccine product-related reaction is caused by the vaccine itself, such as its antigen or adjuvant. A coincidental event occurs after vaccination but has another cause, so the vaccine is not responsible for it.

### Which serious AEFI must be reported promptly?

Serious AEFI include death, hospitalisation, disability and life-threatening events. These need prompt reporting and investigation by the AEFI committee at district level and above, and the case stays open until causality is assessed.

### Which contraindication applies to repeating a vaccine after a severe reaction?

Anaphylaxis or another severe allergic reaction after a previous dose of the same vaccine, or after one of its components, contraindicates repeating that vaccine. Moderate or severe acute illness is only a precaution, which means vaccination is deferred until the child recovers.

### Does a mild fever after vaccination need an AEFI report?

A mild fever or local soreness is an expected, common reaction and usually does not need an AEFI report. Reporting is meant for unusual, serious or unexpected events that follow immunisation.