Measles Vaccine-Associated Rash Illness in China: An Emerging Issue in the Process of Measles Elimination.

Along with the implementation of the measles case-based surveillance, measles vaccine-associated rash illness (VARI) cases were detected in China. To better understand the characteristics of VARI, 101 VARI cases confirmed by measles virus genotyping in 2011-2018 were analyzed in this study. With the decrease in measles incidence, the detection rate of VARI cases increased among the cases confirmed by genotyping. Compared with genotype H1 wild-type measles, VARI occurred throughout the year without obvious seasonal distribution. Infants/children aged 8-23 months were the main population of VARI. VARI mainly occurred within 14 days after measles vaccination. The number of VARI cases peaked on the 8th day after measles vaccination, which was later than that of genotype H1 wild-type measles cases with a measles vaccination history. VARI presents clinical symptoms similar to measles. The frequencies of the "3Cs", Koplik spots and complications in VARI cases were significantly lower than those in wild-type measles cases. In total, 94.06% sequences from VARI cases were identical to measles vaccine strain S191 in the C-terminal 450 nucleotide sequence of the nucleoprotein (N-450) gene. A few substitutions were found in N-450 sequences of the VARI cases.The confirmation of VARI has become an emerging issue in the process of measles elimination. Rapid confirmation of VARI is critical for measles surveillance and will help to determine the response measures for measles, especially in measles pre-elimination and elimination settings. The suspected measles cases with MCV vaccination were recommend to be detected by the laboratory to identify wild-type measles or VARI.