• Wei-Zhong Zhou, Hye-Won Koo, Xuan-Yi Wang, Jun Zhang, Jin-Kyung Park, Fengcai Zhu, Jacqueline Deen, Camilo J Acosta, Yan Chen, Hua Wang, Claudia M Galindo, Leon Ochiai, Taesung Park, Lorenz von Seidlein, Zhi-Yi Xu, and John D Clemens.
• Jiangsu Provincial Center for Disease Prevention and Control, Nanjing, China.
• Pediatr. Infect. Dis. J. 2007 Nov 1; 26 (11): 1001-5.

ObjectiveTo 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.MethodsA 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.ResultsRevaccination 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).ConclusionWe 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.

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