Epidemiology Of Measles In China And Its Strategy Of Eliminating Measles Immunization

Background China began to implement measles elimination strategy since2006, and made efforts to increase MCV coverage through routine immunization and conduct MV supplementary immunization activities (MV SIA). By September2010, all provinces have finished catch up MV SIA, which covered all of1995-2009birth cohorts. Measles incidence decreased to<1per100,000population in2011and2012. However, measles cases were reported from every province.Objectives To better understand age distribution of measles cases in different time period. To estimate susceptibility to measles of each birth cohort in current population. To know risk factors for measles infection in different age groups. And to provide evidence in developing vaccination strategy of measles elimination for next step.Methods (1) Analyze measles surveillance data by descriptive epidemiology on population distribution.(2) Analyze time-varying population, measles case data and MCV vaccination data from six provinces:three from eastern China (Jiangsu, Shandong and Zhejiang), one from central China (Henan), and two from western China (Yunnan and Gansu), to estimate susceptibility of different birth cohorts in current population by catalytic model.(3) Conduct case control study in above six provinces during January2012through June2013. We investigate all laboratory confirmed measles cases reported from these provinces and3age-matched neighborhood controls for every case. Risk factors were analyzed by conditional logistic regression.(4) Conduct field investigation on a typical measles outbreak to measure the real MCV coverage of2010-2013birth cohorts. A qualitative study on the influential factors for the Immunization Program was conducted.Results (1) Children of0-1year old pronounced the highest incidence each year during1988through2013, followed by2-4years old and5-9years old children. In2013, the incidence (per100,000population) of0-1,2-4,5-9,10-14,15-34and>35years group were50.0,5.6,1.4,0.3,1.2, and0.3, respectively, Measles cases aged2-14years accounted for>70%before2000, which gradually decreased then after, reaching13.7%in2013. By contrast, the0-1year group increased from12.3%to59.4%, and>15years group increased from16.5%to26.9%.(2) Since1980, measles force of infection (FOI) declined in overall magnitude with time and the mode shifts from older children (3-10years olds) to younger individuals (0-1year old). The highest percentage of susceptible were in less than one year old children (52.9%), followed by one year old children (16.7%). In each birth cohort of current3-19years population, susceptible population account for less than5%. In contrast, some birth cohorts of adults include10%-20%susceptibles in Jiangsu, Zhejiang, Shandong and Henan. However, it’s around5%in Yunnan and Gansu province.(3) The case control study reveals that, hospital exposure (amOR value was6.2,7.5, and13.0in<8months,8months through14years, and>15years group) and having migration history (amOR value was2.5,1.6, and1.8in above three age-groups, respectively) were risk factors for measles infection in each area and each age group. Lower educational level (amOR=2.3), and older age in≥5months (amOR=3.8) were risk factors in<8months group. Having no vaccination certificate and missing MCV vaccination (amOR=0.046for1dose:0doses, amOR=0.01for2doses:0doses) were risk factors for the children group. The estimated vaccine effectiveness was≥94%for1dose MCV, and was>98%for2doses of MCV.(4) In the county with an outbreak, the routine immunization coverage of MCV1and MCV2were around85%in2010-2012birth cohorts. There is discrepancy between reported high administrative coverage (≥99.4%) and real immunity gap. The qualitative study reveals that in recent years, whith the shortage of input, the ability of supplying routine immunization service decreased in local level, which resulted in the lower coverage and the rapid accumulation of measles susceptibles in new birth cohorts.Conclusions At present, the majority of measles cases were observed in new birth cohorts after the2010MV SIA and adults. The0-1years old children pronounce the highest force of infection, the highest measles incidence rate, and account for a high proportion among all measles cases. Vaccination of MCV can provide excellent protection. The key point of vaccination strategy for measles elimination is to keep all children be timely vaccinated at8months and18months, especially for migrating children. At the same time, vaccination strategy for adults and6-7months old children should be addressed.