title: Demographic transition and the dynamics of measles in six provinces in China: A modeling study.
abstract: Industrialization and demographic transition generate nonstationary dynamics in human populations that can affect the transmission and persistence of infectious diseases. Decades of increasing vaccination and development have led to dramatic declines in the global burden of measles, but the virus remains persistent in much of the world. Here we show that a combination of demographic transition, as a result of declining birth rates, and reduced measles prevalence, due to improved vaccination, has shifted the age distribution of susceptibility to measles throughout China.
  
  
  
  We fit a novel time-varying catalytic model to three decades of age-specific measles case reporting in six provinces in China to quantify the change in the age-specific force of infection for measles virus over time. We further quantified the impact of supplemental vaccination campaigns on the reduction of susceptible individuals. The force of infection of measles has declined dramatically (90%-97% reduction in transmission rate) in three industrialized eastern provinces during the last decade, driving a concomitant increase in both the relative proportion and absolute number of adult cases, while three central and western provinces exhibited dynamics consistent with endemic persistence (24%-73% reduction in transmission rate). The reduction in susceptible individuals due to supplemental vaccination campaigns is frequently below the nominal campaign coverage, likely because campaigns necessarily vaccinate those who may already be immune. The impact of these campaigns has significantly improved over time: campaigns prior to 2005 were estimated to have achieved less than 50% reductions in the proportion susceptible in the target age classes, but campaigns from 2005 onwards reduced the susceptible proportion by 32%-87%. A limitation of this study is that it relies on case surveillance, and thus inference may be biased by age-specific variation in measles reporting.
  
  
  
  The age distribution of measles cases changes in response to both demographic and vaccination processes. Combining both processes in a novel catalytic model, we illustrate that age-specific incidence patterns reveal regional differences in the progress to measles elimination and the impact of vaccination controls in China. The shift in the age distribution of measles susceptibility in response to demographic and vaccination processes emphasizes the importance of progressive control strategies and measures to evaluate program success that anticipate and react to this transition in observed incidence.
authors.affiliation: School of Public Health, City University of New York, New York, New York, United States of America.
authors.forename: Sheng
authors.initials: S
authors.lastname: Li
authors.affiliation: National Immunization Program, China Centers for Disease Control and Prevention, Beijing, China.
authors.forename: Chao
authors.initials: C
authors.lastname: Ma
authors.affiliation: National Immunization Program, China Centers for Disease Control and Prevention, Beijing, China.
authors.forename: Lixin
authors.initials: L
authors.lastname: Hao
authors.affiliation: National Immunization Program, China Centers for Disease Control and Prevention, Beijing, China.
authors.forename: Qiru
authors.initials: Q
authors.lastname: Su
authors.affiliation: National Immunization Program, China Centers for Disease Control and Prevention, Beijing, China.
authors.forename: Zhijie
authors.initials: Z
authors.lastname: An
authors.affiliation: Jiangsu Provincial Center for Disease Control and Prevention, Nanjing, China.
authors.forename: Fubao
authors.initials: F
authors.lastname: Ma
authors.affiliation: Zhejiang Provincial Center for Disease Control and Prevention, Hangzhou, China.
authors.forename: Shuyun
authors.initials: S
authors.lastname: Xie
authors.affiliation: Shandong Provincial Center for Disease Control and Prevention, Jinan, China.
authors.forename: Aiqiang
authors.initials: A
authors.lastname: Xu
authors.affiliation: Henan Provincial Center for Disease Control and Prevention, Zhengzhou, China.
authors.forename: Yanyang
authors.initials: Y
authors.lastname: Zhang
authors.affiliation: Yunnan Provincial Center for Disease Control and Prevention, Kunming, China.
authors.forename: Zhengrong
authors.initials: Z
authors.lastname: Ding
authors.affiliation: Gansu Provincial Center for Disease Control and Prevention, Lanzhou, China.
authors.forename: Hui
authors.initials: H
authors.lastname: Li
authors.affiliation: Global Immunization Division, Centers for Disease Control and Prevention, Atlanta, Georgia, United States of America.
authors.forename: Lisa
authors.identifier: 0000-0002-4742-2169
authors.initials: L
authors.lastname: Cairns
authors.affiliation: National Immunization Program, China Centers for Disease Control and Prevention, Beijing, China.
authors.forename: Huaqing
authors.initials: H
authors.lastname: Wang
authors.affiliation: National Immunization Program, China Centers for Disease Control and Prevention, Beijing, China.
authors.forename: Huiming
authors.initials: H
authors.lastname: Luo
authors.affiliation: Nation Center for AIDS, China Centers for Disease Control and Prevention, Beijing, China.
authors.forename: Ning
authors.initials: N
authors.lastname: Wang
authors.affiliation: National Immunization Program, China Centers for Disease Control and Prevention, Beijing, China.
authors.forename: Li
authors.initials: L
authors.lastname: Li
authors.affiliation: Center for Infectious Disease Dynamics, Pennsylvania State University, University Park, Pennsylvania, United States of America.
authors.forename: Matthew J
authors.initials: MJ
authors.lastname: Ferrari
mesh_terms: D000328:Adult; D017677:Age Distribution; D002648:Child; D002681:China / Q000453:epidemiology; D006801:Humans; D015994:Incidence; D008457:Measles / Q000453:epidemiology* / Q000517:prevention & control / Q000635:transmission; D008458:Measles Vaccine / Q000627:therapeutic use; D008962:Models, Theoretical; D011157:Population Dynamics; D014611:Vaccination / Q000706:statistics & numerical data
chemical_list: D008458:Measles Vaccine