title: Influenza vaccine effectiveness in preventing hospitalization among Beijing residents in China, 2013-15.
abstract: BACKGROUND
  Estimates of influenza vaccination effectiveness (VE) are valuable for populations where the vaccine has been promoted in order to support vaccination policy and to permit evaluation of vaccination strategies. Such studies would be important for China due to limited data available during seasons when the vaccine strains matched or mismatched the circulating viruses.
  
  
  METHODS
  We conducted a test-negative study in hospitals in Beijing. Patients admitted to five hospitals in the city were enrolled during the winter influenza seasons of 2013-14 and 2014-15. Influenza virus infections were determined by PCR, and influenza vaccination records were extracted from a centralized electronic immunization registry. Influenza VE was estimated by logistic regression adjusting for age group, sex and chronic conditions, and matched by calendar week.
  
  
  RESULTS
  A total of 2368 inpatients were recruited during the study period with a vaccination coverage in the control group of 12.8%. The overall estimate of influenza VE was 46.9% (95% CI: -20.4%, 76.6%) for the 2013-14 season and 5.0% (95% CI: -53.0%, 41.0%) for the 2014-15 season. Estimates of VE were relatively higher in children aged 6-17 years than older persons across two influenza seasons while estimates of VE for both adults and elderly were relatively low.
  
  
  CONCLUSIONS
  Our findings were consistent with expected influenza vaccination effectiveness in seasons when the vaccine matched or mismatched circulating viruses. Strategies to increase influenza vaccine coverage could provide a public health benefit.
authors.affiliation: Division of Infectious Disease, Key Laboratory of Surveillance and Early-Warning on Infectious Disease, Chinese Center for Disease Control and Prevention, Beijing, China.
authors.forename: Ying
authors.initials: Y
authors.lastname: Qin
authors.affiliation: Beijing Center for Disease Prevention and Control, Beijing, China.
authors.forename: Yi
authors.initials: Y
authors.lastname: Zhang
authors.affiliation: School of Public Health, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Hong Kong Special Administrative Region.
authors.forename: Peng
authors.initials: P
authors.lastname: Wu
authors.affiliation: School of Public Health, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Hong Kong Special Administrative Region.
authors.forename: Shuo
authors.initials: S
authors.lastname: Feng
authors.affiliation: Division of Infectious Disease, Key Laboratory of Surveillance and Early-Warning on Infectious Disease, Chinese Center for Disease Control and Prevention, Beijing, China.
authors.forename: Jiandong
authors.initials: J
authors.lastname: Zheng
authors.affiliation: Beijing Center for Disease Prevention and Control, Beijing, China.
authors.forename: Peng
authors.initials: P
authors.lastname: Yang
authors.affiliation: Beijing Center for Disease Prevention and Control, Beijing, China.
authors.forename: Yang
authors.initials: Y
authors.lastname: Pan
authors.affiliation: Beijing Center for Disease Prevention and Control, Beijing, China.
authors.forename: Quanyi
authors.initials: Q
authors.lastname: Wang
authors.affiliation: Division of Infectious Disease, Key Laboratory of Surveillance and Early-Warning on Infectious Disease, Chinese Center for Disease Control and Prevention, Beijing, China.
authors.forename: Luzhao
authors.initials: L
authors.lastname: Feng
authors.affiliation: Beijing Center for Disease Prevention and Control, Beijing, China.
authors.forename: Xinghuo
authors.initials: X
authors.lastname: Pang
authors.affiliation: Foundation for the Promotion of Health and Biomedical Research in the Valencia Region FISABIO - Public Health, Valencia, Spain.
authors.forename: Joan
authors.initials: J
authors.lastname: Puig-Barberà
authors.affiliation: Division of Infectious Disease, Key Laboratory of Surveillance and Early-Warning on Infectious Disease, Chinese Center for Disease Control and Prevention, Beijing, China. Electronic address: yuhj@chinacdc.cn.
authors.forename: Hongjie
authors.initials: H
authors.lastname: Yu
authors.affiliation: School of Public Health, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Hong Kong Special Administrative Region. Electronic address: bcowling@hku.hk.
authors.forename: Benjamin J
authors.initials: BJ
authors.lastname: Cowling
mesh_terms: D000293:Adolescent; D000328:Adult; D000068476:Beijing / Q000453:epidemiology; D002648:Child; D002675:Child, Preschool; D005260:Female; D006760:Hospitalization / Q000706:statistics & numerical data*; D006801:Humans; D007223:Infant; D007252:Influenza Vaccines / Q000627:therapeutic use*; D007251:Influenza, Human / Q000517:prevention & control*; D016015:Logistic Models; D008297:Male; D008875:Middle Aged; D012621:Seasons; D018571:Sentinel Surveillance; D014611:Vaccination / Q000706:statistics & numerical data; D055815:Young Adult
chemical_list: D007252:Influenza Vaccines
keywords: Hospitalization; Influenza vaccine; Test negative design; Vaccine effectiveness