A 12-month-old child with a history of anaphylaxis to egg protein is due for MMR vaccination. The parents are concerned about vaccine safety. What is the most appropriate investigation to guide the decision regarding MMR vaccination in this child?

Explanation

## Investigation of Choice: Skin Prick Test (SPT) or Intradermal Test ### Clinical Context MMR vaccine contains trace amounts of egg protein (from the culture medium used in vaccine production). Children with egg allergy require careful assessment before MMR vaccination to determine if the egg content poses a risk. ### Why SPT/Intradermal Test is the Answer **Key Point:** Skin testing is the gold standard to assess the severity and type of egg allergy: - **Negative SPT** → MMR can be given safely in routine setting - **Positive SPT with history of anaphylaxis** → MMR should be given in a medical facility with resuscitation equipment available **High-Yield:** According to IAP guidelines, most children with egg allergy can safely receive MMR vaccine because: 1. The egg protein content in MMR is minimal 2. The allergen is inactivated during vaccine production 3. SPT helps stratify risk and guide administration approach ### Risk Stratification Based on Allergy History | Allergy Type | SPT Result | MMR Administration | |---|---|---| | Mild egg allergy (urticaria) | Negative | Routine clinic setting | | Mild egg allergy (urticaria) | Positive | Medical facility with observation | | Anaphylaxis to egg | Negative | Routine clinic setting | | Anaphylaxis to egg | Positive | Medical facility with IM adrenaline ready | **Clinical Pearl:** The presence of anaphylaxis history does NOT automatically contraindicate MMR. SPT helps differentiate true IgE-mediated allergy from other reactions, enabling safe vaccination. ### Decision Algorithm ```mermaid flowchart TD A[Child with egg allergy history due for MMR]:::outcome --> B[Perform SPT for egg protein]:::action B --> C{SPT Positive?}:::decision C -->|No| D[MMR in routine clinic]:::action C -->|Yes| E{History of anaphylaxis?}:::decision E -->|No| F[MMR in medical facility with observation]:::action E -->|Yes| G[MMR in medical facility with IM adrenaline ready]:::action D --> H[Safe vaccination achieved]:::outcome F --> H G --> H ``` **Mnemonic:** **SAFE EGG** = **S**kin test, **A**ssess severity, **F**acility-based if needed, **E**phedrine/adrenaline ready, **G**ive vaccine, **G**ood outcome.