In an infant who developed urticaria 4 days after measles‑rubella vaccination and was treated with cetirizine, then a 5‑day course of prednisone with a slight increase in cetirizine dose, why did the hives recur after stopping therapy and what is the most effective management for vaccine‑induced urticaria?

Post-MR Vaccine Urticaria with Recurrence After Steroid Withdrawal

Why the Hives Recurred

The urticaria recurred because the 5-day prednisone course was too short to suppress the ongoing vaccine-induced immune response, which typically peaks 7-12 days post-vaccination and can persist for several weeks. 1, 2

The timeline is critical here:

• Day 4 post-vaccination: Urticaria appeared, which is actually earlier than the typical vaccine-related rash that occurs at 7-10 days 3, 2
• Day 5: Prednisone started for only 5 days
• After medication stopped: Hives returned because the underlying immune response was still active

The problem is that vaccine-induced hypersensitivity reactions—particularly urticaria from MMR/MR vaccines—represent an ongoing immune response to vaccine components (most commonly gelatin, not egg antigens) that can last 2-4 weeks. 3, 1, 4 A short steroid burst simply masks symptoms temporarily without addressing the full duration of the reaction. 1

Most Effective Management Strategy

Discontinue the prednisone and manage with antihistamines alone for a longer duration (2-4 weeks) until the vaccine-induced immune response naturally resolves. 1, 2

Specific Treatment Protocol:

Antihistamine therapy:

• Continue cetirizine at the increased dose (or use loratadine as alternative) 1
• Administer daily for 2-4 weeks minimum, not just until hives clear 1, 2
• Do NOT stop antihistamines abruptly when hives resolve; taper over 3-5 days to prevent rebound 1

Avoid steroids:

• The CDC and AAP guidelines do not recommend systemic corticosteroids for simple vaccine-related urticaria 3, 1, 4
• Steroids are reserved only for severe reactions with respiratory distress, oropharyngeal edema, or hypotension—none of which are present here 1, 4
• Short steroid courses create a rebound phenomenon when the underlying allergic process outlasts the medication 1

Monitoring Requirements:

Watch for progression to anaphylaxis (though extremely rare at <1 per million doses): 3, 4

• Difficulty breathing
• Throat swelling
• Hypotension
• Wheezing

If any of these develop, this becomes a medical emergency requiring epinephrine. 4

Critical Pitfall to Avoid

The most common error is stopping antihistamines too early when hives temporarily clear. 1, 2 The vaccine-induced immune response continues for weeks regardless of visible symptoms. Antihistamines must be continued for the full 2-4 week period to cover the entire duration of viral replication and immune activation. 2, 4

Important Consideration: Cetirizine Paradox

One rare but documented phenomenon: cetirizine itself can occasionally cause urticaria in susceptible individuals. 5 If the hives persist beyond 4 weeks despite adequate antihistamine therapy, consider switching to a different antihistamine class (loratadine, fexofenadine) to rule out paradoxical drug-induced urticaria. 5

Future Vaccination Decisions

For the second MR dose: 1, 4

• Urticaria alone (without anaphylaxis) is NOT a contraindication to future doses 3, 1, 4
• The child can receive the second dose, but with precautions: 1
  • Administer in a setting with epinephrine immediately available 4
  • Observe for 30 minutes post-vaccination 1
  • Consider pre-medicating with antihistamines 1 hour before vaccination 1
  • If gelatin allergy is suspected, skin testing for gelatin sensitivity can be considered before the next dose 3, 1

Key reassurance point: The risk of thrombocytopenia and serious complications from natural measles or rubella infection is 10-100 times greater than the risk from the vaccine. 2, 4 The benefits of completing the vaccination series far outweigh the risk of recurrent urticaria. 1, 4