title: An outbreak of type π vaccine-derived poliovirus in Sichuan province, China: emergence and circulation in an under-immunized population.
abstract: BACKGROUND
  During August 2011-February 2012, an outbreak of type Π circulating vaccine-derived poliovirus (cVDPVs) occurred in Sichuan Province, China.
  
  
  METHODS
  A field investigation of the outbreak was conducted to characterize outbreak isolates and to guide emergency response. Sequence analysis of poliovirus capsid protein VP1 was performed to determine the viral propagation, and a coverage survey was carried out for risk assessment.
  
  
  RESULTS
  One clinical compatible polio case and three VDPV cases were determined in Ngawa County, Ngawa Tibetan and Qiang Autonomous Prefecture, Sichuan Province. Case patients were unimmunized children, 0.8-1 years old. Genetic sequencing showed that the isolates diverged from the VP1 region of the type Π Sabin strain by 5-12 nucleotides (nt) and shared the same 5 nt VP1 substitutions, which indicate single lineage of cVDPVs. Of the 7 acute flaccid paralysis cases (all>6 months) reported in Ngawa Prefecture in 2011, 4 (57.1%) cases (including 2 polio cases) did not receive oral attenuated poliovirus vaccine. Supplementary immunization activities (SIAs) were conducted in February-May, 2012, and the strain has not been isolated since.
  
  
  CONCLUSIONS
  High coverage of routine immunization should be maintained among children until WPV transmission is globally eradicated. Risk assessments should be conducted regularly to pinpoint high risk areas or subpopulations, with SIAs developed if necessary.
authors.affiliation: Chinese Center for Disease Control and Prevention, Nanwei Rd 27#, Xicheng District, Beijing 100050, PR China; Peking University Clinical Research Institute, Xueyuan Rd 38#, Haidian District, Beijing 100191, PR China.
authors.forename: Hai-Bo
authors.initials: HB
authors.lastname: Wang
authors.affiliation: Sichuan Provincial Center for Disease Control and Prevention, Zhongxue Road 6#, Chengdu City, Sichuan Province 610041, PR China.
authors.forename: Gang
authors.initials: G
authors.lastname: Fang
authors.affiliation: Chinese Center for Disease Control and Prevention, Nanwei Rd 27#, Xicheng District, Beijing 100050, PR China.
authors.forename: Wen-Zhou
authors.initials: WZ
authors.lastname: Yu
authors.affiliation: Sichuan Provincial Center for Disease Control and Prevention, Zhongxue Road 6#, Chengdu City, Sichuan Province 610041, PR China.
authors.forename: Fei
authors.initials: F
authors.lastname: Du
authors.affiliation: Chinese Center for Disease Control and Prevention, Nanwei Rd 27#, Xicheng District, Beijing 100050, PR China.
authors.forename: Chun-Xiang
authors.initials: CX
authors.lastname: Fan
authors.affiliation: Sichuan Provincial Center for Disease Control and Prevention, Zhongxue Road 6#, Chengdu City, Sichuan Province 610041, PR China.
authors.forename: Qing-Lian
authors.initials: QL
authors.lastname: Liu
authors.affiliation: Chinese Center for Disease Control and Prevention, Nanwei Rd 27#, Xicheng District, Beijing 100050, PR China.
authors.forename: Li-Xin
authors.initials: LX
authors.lastname: Hao
authors.affiliation: Sichuan Provincial Center for Disease Control and Prevention, Zhongxue Road 6#, Chengdu City, Sichuan Province 610041, PR China.
authors.forename: Yu
authors.initials: Y
authors.lastname: Liu
authors.affiliation: Chinese Center for Disease Control and Prevention, Nanwei Rd 27#, Xicheng District, Beijing 100050, PR China.
authors.forename: Jing-Shan
authors.initials: JS
authors.lastname: Zheng
authors.affiliation: Sichuan Provincial Center for Disease Control and Prevention, Zhongxue Road 6#, Chengdu City, Sichuan Province 610041, PR China.
authors.forename: Zhi-Ying
authors.initials: ZY
authors.lastname: Qin
authors.affiliation: Chinese Center for Disease Control and Prevention, Nanwei Rd 27#, Xicheng District, Beijing 100050, PR China.
authors.forename: Wei
authors.initials: W
authors.lastname: Xia
authors.affiliation: Ngawa Tibetan and Qiang Autonomous Prefectural Center for Disease Control and Prevention, Meigu Street 178#, Maerkang County, Ngawa Tibetan and Qiang Autonomous Prefecture, Sichuan Province 624000, PR China.
authors.forename: Shi-Yue
authors.initials: SY
authors.lastname: Zhang
authors.affiliation: Chinese Center for Disease Control and Prevention, Nanwei Rd 27#, Xicheng District, Beijing 100050, PR China.
authors.forename: Zun-Dong
authors.initials: ZD
authors.lastname: Yin
authors.affiliation: Ngawa Tibetan and Qiang Autonomous Prefectural Center for Disease Control and Prevention, Meigu Street 178#, Maerkang County, Ngawa Tibetan and Qiang Autonomous Prefecture, Sichuan Province 624000, PR China.
authors.forename: Qiong
authors.initials: Q
authors.lastname: Jing
authors.affiliation: Chinese Center for Disease Control and Prevention, Nanwei Rd 27#, Xicheng District, Beijing 100050, PR China.
authors.forename: Yan-Xia
authors.initials: YX
authors.lastname: Zhang
authors.affiliation: Chengdu City Center for Disease Control and Prevention, Longxiang Rd 4#, Chengdu City, Sichuan Province 610041, PR China.
authors.forename: Rong-Na
authors.initials: RN
authors.lastname: Huang
authors.affiliation: Chengdu City Center for Disease Control and Prevention, Longxiang Rd 4#, Chengdu City, Sichuan Province 610041, PR China.
authors.forename: Ru-Pei
authors.initials: RP
authors.lastname: Yang
authors.affiliation: Sichuan Provincial Center for Disease Control and Prevention, Zhongxue Road 6#, Chengdu City, Sichuan Province 610041, PR China.
authors.forename: Wen-Bin
authors.initials: WB
authors.lastname: Tong
authors.affiliation: Sichuan Provincial Center for Disease Control and Prevention, Zhongxue Road 6#, Chengdu City, Sichuan Province 610041, PR China.
authors.forename: Qi
authors.initials: Q
authors.lastname: Qi
authors.affiliation: Sichuan Provincial Center for Disease Control and Prevention, Zhongxue Road 6#, Chengdu City, Sichuan Province 610041, PR China.
authors.forename: Xu-Jing
authors.initials: XJ
authors.lastname: Guan
authors.affiliation: Sichuan Provincial Center for Disease Control and Prevention, Zhongxue Road 6#, Chengdu City, Sichuan Province 610041, PR China.
authors.forename: Yu-Lin
authors.initials: YL
authors.lastname: Jing
authors.affiliation: Sichuan Provincial Center for Disease Control and Prevention, Zhongxue Road 6#, Chengdu City, Sichuan Province 610041, PR China.
authors.forename: Qian-Li
authors.initials: QL
authors.lastname: Ma
authors.affiliation: Sichuan Provincial Center for Disease Control and Prevention, Zhongxue Road 6#, Chengdu City, Sichuan Province 610041, PR China.
authors.forename: Jin
authors.initials: J
authors.lastname: Wang
authors.affiliation: Sichuan Provincial Center for Disease Control and Prevention, Zhongxue Road 6#, Chengdu City, Sichuan Province 610041, PR China.
authors.forename: Xiao-Zhen
authors.initials: XZ
authors.lastname: Ma
authors.affiliation: Sichuan Provincial Center for Disease Control and Prevention, Zhongxue Road 6#, Chengdu City, Sichuan Province 610041, PR China.
authors.forename: Na
authors.initials: N
authors.lastname: Chen
authors.affiliation: Sichuan Provincial Center for Disease Control and Prevention, Zhongxue Road 6#, Chengdu City, Sichuan Province 610041, PR China.
authors.forename: Hong-Ru
authors.initials: HR
authors.lastname: Zheng
authors.affiliation: Sichuan Provincial Center for Disease Control and Prevention, Zhongxue Road 6#, Chengdu City, Sichuan Province 610041, PR China.
authors.forename: Yin-Qiao
authors.initials: YQ
authors.lastname: Li
authors.affiliation: Chinese Center for Disease Control and Prevention, Nanwei Rd 27#, Xicheng District, Beijing 100050, PR China.
authors.forename: Chao
authors.initials: C
authors.lastname: Ma
authors.affiliation: Chinese Center for Disease Control and Prevention, Nanwei Rd 27#, Xicheng District, Beijing 100050, PR China.
authors.forename: Qi-Ru
authors.initials: QR
authors.lastname: Su
authors.affiliation: National Center for AIDS/STD Control and Prevention, Chinese Center for Disease Control and Prevention, Nanwei Rd 27#, Xicheng District, Beijing 100050, PR China.
authors.forename: Kathleen H
authors.initials: KH
authors.lastname: Reilly
authors.affiliation: Chinese Center for Disease Control and Prevention, Nanwei Rd 27#, Xicheng District, Beijing 100050, PR China.
authors.forename: Hui-Ming
authors.initials: HM
authors.lastname: Luo
authors.affiliation: Sichuan Provincial Center for Disease Control and Prevention, Zhongxue Road 6#, Chengdu City, Sichuan Province 610041, PR China.
authors.forename: Xian-Ping
authors.initials: XP
authors.lastname: Wu
authors.affiliation: Chinese Center for Disease Control and Prevention, Nanwei Rd 27#, Xicheng District, Beijing 100050, PR China.
authors.forename: Ning
authors.initials: N
authors.lastname: Wen
authors.affiliation: Chinese Center for Disease Control and Prevention, Nanwei Rd 27#, Xicheng District, Beijing 100050, PR China.
authors.forename: Wei-Zhong
authors.initials: WZ
authors.lastname: Yang
mesh_terms: D000293:Adolescent; D002648:Child; D002675:Child, Preschool; D002681:China / Q000453:epidemiology; D004196:Disease Outbreaks / Q000517:prevention & control; D005260:Female; D006801:Humans; D007114:Immunization / Q000706:statistics & numerical data*; D007223:Infant; D008297:Male; D010243:Paralysis / Q000453:epidemiology; D011051:Poliomyelitis / Q000453:epidemiology* / Q000517:prevention & control* / Q000635:transmission; D017955:Poliovirus / Q000276:immunology* / Q000502:physiology; D023321:Poliovirus Vaccines / Q000276:immunology*
chemical_list: D023321:Poliovirus Vaccines