What is the cause of a rash after measles-mumps-rubella vaccination?

Surveillance and laboratory confirmation of measles will increase in import ance as Australia implements enhanced measles control. We describe a 17-mon th-old child with fever and rash after measles-mumps-rubella vaccination. D etection of vaccine-strain measles virus in his urine by polymerase chain r eaction confirmed the diagnosis of a vaccine reaction rather than wildtype measles. We propose that measles virus should be sought and identified as v accine or wild-type virus when the relationship between vaccination and mea sles-like illness is uncertain.