As far as we know, this is the first measles outbreak caused by imported D8 genotype in Jiangsu province, and the fourth in China. Further epidemiological investigation showed that neither of the two patients reported herein had received measles vaccination. The first D8 case was an eight-month old child from Shanghai in 2012, with no previous measles vaccination, and the second outbreak was in Beijing in 2013, with two adult cases, for whom no information on measles vaccination could be gathered. All of these reports suggest that an immunity gap among all imported D8 genotype cases, which is still an important factor for transmitting measles virus. It is therefore necessary to implement supplement activity of measles immunization target adult with immunity gap.
Population density is a major determinant of attack rates and transmission of measles virus. In China, almost of all imported measles cases occurred in economically developed regions and border regions. Frequent migration and higher population density make these regions more vulnerable than others in China, as all adults got imported measles virus infection in venues with higher population density such as school, hospital, and fabric market. Therefore, more attention should be drawn to measles surveillance in regions and venues with high population migration and density, especially in epidemic seasons.