title: Effect of dosage on immunogenicity of a Vi conjugate vaccine injected twice into 2- to 5-year-old Vietnamese children.
abstract: In a double-blind, randomized, and placebo-controlled previous trial, the efficacy of Vi-rEPA for typhoid fever in 2- to 5-year-olds was 89.0% for 46 months. Vi-rEPA contained 25 microg of Vi and induced a greater-than-eightfold rise in immunoglobulin G (IgG) anti-Vi in all of the vaccinees tested. In this investigation, we conducted a dosage-immunogenicity study of 5, 12.5, and 25 microg of Vi-rEPA in this age group. Two doses of Vi-rEPA were injected 6 weeks apart. Blood samples were taken before and at 10 weeks (4 weeks after the second injection) and 1 year later. All postimmunization geometric mean (GM) levels were higher than the preimmune levels (P < 0.0001). At 10 weeks, the GM IgG anti-Vi level elicited by 25 microg (102 EU/ml) was higher than those elicited by 12.5 microg (74.7 EU/ml) and 5 microg (43 EU/ml) (P < 0.004): all of the children had > or = 3.52 EU/ml (estimated minimum protective level). One year later, the levels declined about sevenfold (13.3 and 11.3 versus 6.43 EU/ml, P < 0.0001) but remained significantly higher than the preimmune levels (P < 0.0001), and >96% of the children had a greater-than-eightfold rise. This study also confirmed the safety and consistent immunogenicity of the four lots of Vi-rEPA used in this and previous trials.
authors.affiliation: Diarrhea Diseases Epidemiology and Field Research Section, National Institute of Hygiene and Epidemiology, Hanoi, Veitnam.
authors.forename: Do Gia
authors.initials: DG
authors.lastname: Canh
authors.forename: Feng-ying Kimi
authors.initials: FY
authors.lastname: Lin
authors.forename: Vu Dinh
authors.initials: VD
authors.lastname: Thiem
authors.forename: Dang Duc
authors.initials: DD
authors.lastname: Trach
authors.forename: Nguyen Dinh
authors.initials: ND
authors.lastname: Trong
authors.forename: Nguyen Duc
authors.initials: ND
authors.lastname: Mao
authors.forename: Steven
authors.initials: S
authors.lastname: Hunt
authors.forename: Rachel
authors.initials: R
authors.lastname: Schneerson
authors.forename: John B
authors.initials: JB
authors.lastname: Robbins
authors.forename: Chiayung
authors.initials: C
authors.lastname: Chu
authors.forename: Joseph
authors.initials: J
authors.lastname: Shiloach
authors.forename: Dolores A
authors.initials: DA
authors.lastname: Bryla
authors.forename: Marie-Claude
authors.initials: MC
authors.lastname: Bonnet
authors.forename: Dominique
authors.initials: D
authors.lastname: Schulz
authors.forename: Shousun C
authors.initials: SC
authors.lastname: Szu
mesh_terms: D036002:ADP Ribose Transferases / Q000008:administration & dosage* / Q000009:adverse effects / Q000276:immunology; D000907:Antibodies, Bacterial / Q000097:blood*; D001427:Bacterial Toxins / Q000008:administration & dosage* / Q000009:adverse effects / Q000276:immunology; D002675:Child, Preschool; D004306:Dose-Response Relationship, Immunologic; D004311:Double-Blind Method; D005098:Exotoxins / Q000008:administration & dosage* / Q000009:adverse effects / Q000276:immunology; D006801:Humans; D007074:Immunoglobulin G / Q000097:blood; D008297:Male; D011135:Polysaccharides, Bacterial / Q000008:administration & dosage* / Q000009:adverse effects / Q000276:immunology*; D012485:Salmonella typhi / Q000276:immunology*; D014435:Typhoid Fever / Q000517:prevention & control; D014436:Typhoid-Paratyphoid Vaccines / Q000008:administration & dosage* / Q000009:adverse effects / Q000276:immunology*; D018074:Vaccines, Conjugate / Q000008:administration & dosage / Q000009:adverse effects / Q000276:immunology; D014744:Vietnam; D037521:Virulence Factors / Q000008:administration & dosage* / Q000009:adverse effects / Q000276:immunology; D000097668:Pseudomonas aeruginosa Exotoxin A
chemical_list: D036002:ADP Ribose Transferases; D000907:Antibodies, Bacterial; D001427:Bacterial Toxins; D005098:Exotoxins; D007074:Immunoglobulin G; D011135:Polysaccharides, Bacterial; D014436:Typhoid-Paratyphoid Vaccines; D018074:Vaccines, Conjugate; D037521:Virulence Factors; D000097668:Pseudomonas aeruginosa Exotoxin A; C057664:Vi polysaccharide vaccine, typhoid