A 15-month-old child presents 10 days after receiving MMR vaccine with fever and petechiae but no lymphadenopathy or organomegaly. Platelet count is 32,000/μL. This most likely represents:
- A Measles inclusion body encephalitis
- B Immune thrombocytopenic purpura (ITP) following MMR — most common serious adverse event of MMR vaccine ✓
- C MMR-associated aseptic meningitis due to mumps component
- D Severe combined immunodeficiency presenting after live vaccine
Correct answer: B. Immune thrombocytopenic purpura (ITP) following MMR — most common serious adverse event of MMR vaccine
Explanation
Post-MMR immune thrombocytopenic purpura (ITP) is the most common serious adverse event following MMR vaccination, occurring in approximately 1 in 30,000–40,000 doses, typically 6–14 days after vaccination. It is usually mild, self-limiting, and carries an excellent prognosis. The mechanism is cross-reactive immune response against platelet antigens. It is distinct from the rare risk of vaccine-strain viral encephalitis. SCID may present after live vaccines as vaccine-strain disseminated disease, but would be far more severe.
Reference: Ghai Essential Pediatrics, 10th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.