Revaccination with locally-produced vi typhoid polysaccharide vaccine among chinese school-aged children: safety and immunogenicity findings.
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.
Zhou
Wei-Zhong
WZ
Jiangsu Provincial Center for Disease Prevention and Control, Nanjing, China.
Koo
Hye-Won
HW
Wang
Xuan-Yi
XY
Zhang
Jun
J
Park
Jin-Kyung
JK
Zhu
Fengcai
F
Deen
Jacqueline
J
Acosta
Camilo J
CJ
Chen
Yan
Y
Wang
Hua
H
Galindo
Claudia M
CM
Ochiai
Leon
L
Park
Taesung
T
von Seidlein
Lorenz
L
Xu
Zhi-Yi
ZY
Clemens
John D
JD
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
D000907:Antibodies, Bacterial; D011135:Polysaccharides, Bacterial; D014436:Typhoid-Paratyphoid Vaccines; C057664:Vi polysaccharide vaccine, typhoid