Despite the fact that the highly efficient measles vaccine has significantly lowered the prevalence of measles, cases and outbreaks of measles continue to occur in vaccinated populations due to vaccination failure. The study describes an epidemic in which two cases had previous indications of measles immunity and subsequently one of them infected an unprotected contact. It was possible to gather clinical and epidemiological data. Serum samples were obtained to test for measles-specific immunoglobulin M (IgM), IgG, and IgG avidity. To test for measles virus RNA, throat swabs were collected. Two measles cases occurred on the 18th and 20th of January, both while working at a hospital in Beijing and having had one dose of MCV in the previous five years. Out of the 102 contacts, one additional case with close, long-term co-exposure to case 1 was later recorded. There were no further occurrences of measles among the 15 contacts of case 3. Cases 1 and 2 both exhibited high-avidity IgG antibodies, indicating a subsequent immunological response, and acquired a changed clinical presentation.

This is the second case since a New York City epidemic that indicates a vaccinated person with confirmed secondary vaccination failure (SVF) can transmit measles. Because the epidemic consisted of a succession of uncommon incidents, we may infer that the SVF people involved in the measles transmission chain are unlikely to endanger measles eradication. The significance of herd immunity in avoiding transmission and sensitive surveillance operations in the event of a misdiagnosis is stressed.