A 10-month-old child develops high fever, rash, and Koplik's spots 3 weeks after receiving MR vaccine. The MOST likely explanation is:
- A Vaccine failure due to maternal antibody interference at 9 months
- B Modified measles (vaccine-modified disease) from partial immunity
- C Wild-type measles infection acquired before vaccine-induced immunity developed ✓
- D Vaccine-associated measles from reversion of attenuated strain
Correct answer: C. Wild-type measles infection acquired before vaccine-induced immunity developed
Explanation
Koplik's spots are pathognomonic of wild-type measles and do not occur in vaccine-modified disease or with the attenuated vaccine strain. Vaccine-induced immunity takes 10–14 days to develop; if the child was already incubating wild measles at vaccination, they will develop full clinical measles. The 3-week timeline post-vaccination corresponds to measles incubation (7–21 days), consistent with pre-existing exposure. Vaccine-modified measles is milder without Koplik's spots.
Reference: Ghai Essential Pediatrics, 10th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.