title: Revaccination with locally-produced vi typhoid polysaccharide vaccine among chinese school-aged children: safety and immunogenicity findings.
abstract: OBJECTIVE
  To evaluate the safety and immunogenicity of revaccination with locally-produced Vi polysaccharide vaccine 3 years after the first dose in Chinese children aged 9 to 14 years.
  
  
  METHODS
  A randomized, placebo-controlled trial was conducted in Suzhou, Jiangsu, China. Six hundred and sixty-seven eligible children who had previously received a primary dose of Vi vaccine were randomly assigned to receive 1 dose of 30 mug Vi vaccine or placebo. In addition, 331 eligible children received 1 dose of Vi polysaccharide vaccine as a primary vaccination. Adverse events were followed for 28 days after vaccination. Serum samples were collected from a subgroup of participants on day 0 and day 28, and Vi antibodies were analyzed using a passive hemagglutination method.
  
  
  RESULTS
  Revaccination was found to be safe and immunogenic. No severe adverse events were observed. A significant increase in antibody titers after vaccination was observed among children who had and had not been previously vaccinated. Twenty-eight days after injection, the seropositive rate was 79% in both revaccination and primary injection groups; the geometric mean antibody titer was 1:40 in the primary injection group and 1:29 in the revaccination group (P = 0.24). Although the difference of attained geometric mean titers in follow-up sera was not significantly different in these 2 groups, the fold-rise of these titers from baseline was significantly higher in the primary injection group than in the revaccination group (7.7 versus 3.1, P < 0.001).
  
  
  CONCLUSIONS
  We found that revaccination using the locally produced Vi polysaccharide vaccine among Chinese school-aged children was safe and increased antibody titers. Revaccination can be used to extend the duration of protection provided by Vi polysaccharide vaccine.
authors.affiliation: Jiangsu Provincial Center for Disease Prevention and Control, Nanjing, China.
authors.forename: Wei-Zhong
authors.initials: WZ
authors.lastname: Zhou
authors.forename: Hye-Won
authors.initials: HW
authors.lastname: Koo
authors.forename: Xuan-Yi
authors.initials: XY
authors.lastname: Wang
authors.forename: Jun
authors.initials: J
authors.lastname: Zhang
authors.forename: Jin-Kyung
authors.initials: JK
authors.lastname: Park
authors.forename: Fengcai
authors.initials: F
authors.lastname: Zhu
authors.forename: Jacqueline
authors.initials: J
authors.lastname: Deen
authors.forename: Camilo J
authors.initials: CJ
authors.lastname: Acosta
authors.forename: Yan
authors.initials: Y
authors.lastname: Chen
authors.forename: Hua
authors.initials: H
authors.lastname: Wang
authors.forename: Claudia M
authors.initials: CM
authors.lastname: Galindo
authors.forename: Leon
authors.initials: L
authors.lastname: Ochiai
authors.forename: Taesung
authors.initials: T
authors.lastname: Park
authors.forename: Lorenz
authors.initials: L
authors.lastname: von Seidlein
authors.forename: Zhi-Yi
authors.initials: ZY
authors.lastname: Xu
authors.forename: John D
authors.initials: JD
authors.lastname: Clemens
mesh_terms: D000293:Adolescent; D000907:Antibodies, Bacterial / Q000097:blood*; D002648:Child; D002681:China; D004311:Double-Blind Method; D005260:Female; D006801:Humans; D007117:Immunization, Secondary; D008297:Male; D011135:Polysaccharides, Bacterial / Q000008:administration & dosage / Q000009:adverse effects* / Q000276:immunology*; D012485:Salmonella typhi / Q000276:immunology; D016896:Treatment Outcome; D014435:Typhoid Fever / Q000517:prevention & control*; D014436:Typhoid-Paratyphoid Vaccines / Q000008:administration & dosage / Q000009:adverse effects* / Q000276:immunology*; D014611:Vaccination
chemical_list: D000907:Antibodies, Bacterial; D011135:Polysaccharides, Bacterial; D014436:Typhoid-Paratyphoid Vaccines; C057664:Vi polysaccharide vaccine, typhoid